I am time traveller with aim to make world better. Last time I went to the past, all I heard was: "Kill Hitler!"

So I went to the past and I must tell you, April 1945 was pretty loud in Berlin!

After I returned back, telling everyone that I shot Hitler to the head on 30th April 1945, all I heard was: "You did not do any preparation? Seriously?!"

So this time (pun intended), I want USA to be switching to SI Units. Why? Because I hate Fahrenheits. I hate hearing "Its just 20 miles away" without knowing how far it actually is. So, I decided to travel to the past and changing USA measurement system to lovely Celsius's and kilometers.

However, I am not sure, if I can do it in single-event trip. Thats why I am asking this question:

Can you make USA to use International system of units in single-event scenario?

  • Must be single-event scenario. My machine has energy left just for one return trip
  • Must be caused by external action or non-action (e.g. forcing someone not to do X)
  • Must result by United States of America using officially SI Units.
  • Since some may say that US already defines measurements based on SI units, I care more about "commoners" than for official definitions.
  • You may assume I am able to convince up to ten people (if group meeting needs to be done)
  • You may assume no one will think that I am time traveller (I will wear proper clothing and talk proper language, including its pronunciation)
  • Assume I can stay up to one month in the past, before I need to return back to my own time.
  • I want to return back to my own time alive. Therefore, I do not want to do anything involving risking my life (examples: Helping to fight off someone or jumping in front of a person to stop the killing bullet)
  • I do not care about historical consequences. As long as there will be a state recognized as the USA, placed somewhere in the current USA-area and it will be having people using "normal" units, that is all I care about.
  • No, I will not tell you how my time machine works and if it has any flaws.
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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ Commented Oct 15, 2018 at 16:08
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    $\begingroup$ Don't pretend this is fiction. You have a time-machine!! Well, good luck with the mission. I suspect killing Hitler was far easier than getting America to ditch it's beloved units of measure. When you're done, come to the UK, we still use miles, and many still cling to feet and inches, despite SI units being taught in schools for over 40 years $\endgroup$
    – Greg Woods
    Commented Oct 19, 2018 at 16:15
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    $\begingroup$ Well, this would have helped the Mars Climate Orbiter, so +1 from me $\endgroup$
    – Zommuter
    Commented Oct 20, 2018 at 9:21
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    $\begingroup$ I assume "Kill Columbus" does not count? $\endgroup$ Commented Oct 21, 2018 at 22:21
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    $\begingroup$ I do hope you didn't make your time machine in the States, or with any US-made components. It would be a real shame if you were successful only to return to your own time and find that the 3/8" retrieval flanges on your excursion module no longer mated correctly with the 10mm docking nubbins on the base unit, leading to a temporal rift that wiped out both timelines. $\endgroup$ Commented Oct 22, 2018 at 15:05

13 Answers 13


Stop one ship from either sailing into a storm or (later) being taken over by pirates.

In 1793, Thomas Jefferson ordered a set of instruments from France that would let the US calibrate to SI units, but the ship hit a storm at sea, blowing his ship into the Caribbean. There it was attacked by pirates (British privateers). The materials never arrived. By the time France sent a second set, US had a new Secretary of State who didn’t like metric system.

You either need to delay the ship departure (so it misses the storm) or help take down the pirates. Minimal intervention.


Background information for the well-prepared time traveller

  • Jefferson, Congress, and weights and measures, with mention of the missed window of opportunity on pp. 21–22:
    • Charles F. Treat (1971). "Toward a more perfect uniformity (1607–1860)". A History of the Metric System Controversy in the United States: U.S. Metric Study Interim Report, Volume 13. U.S. Department of Commerce, National Bureau of Standards.
  • Joseph Dombey, the Frenchman with the task of delivering the first set of official copies of the standards to Jefferson:
  • Louis Chambaud (1787). Chambaud's dictionary : French and English and English and French. Containing The Signification of Words, with their different Uses ; The Terms of Arts, Sciences, and Trades ; and The Constructions, Forms of Speech, Idioms, and Proverbs used in both Languages. London: A. Strahan, T. Cadell, and P. Elmsley. OCLC 642509248.
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    $\begingroup$ Seriously? I've never heard about this, this is awesome. $\endgroup$
    – Andon
    Commented Oct 14, 2018 at 15:11
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    $\begingroup$ Also worth noting, this can be done without significant personal risk by changing the departure date of the ship. Look into the historical weather, and convince them to leave earlier or later. Not encountering the storm means they'd stay on course and be a more boring trip. $\endgroup$
    – Andon
    Commented Oct 14, 2018 at 15:14
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    $\begingroup$ Could you add a few more details like the time? I can't read that article and maybe at one point it is totally gone. $\endgroup$
    – PlasmaHH
    Commented Oct 15, 2018 at 16:11
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    $\begingroup$ Particularly bearing in mind @Andon's suggestion, this is a pretty good example of a minimum intervention to achieve a specific effect via time travel. $\endgroup$
    – bgvaughan
    Commented Oct 15, 2018 at 18:45
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    $\begingroup$ No wait, dont stop that ship! It took me great effort to travel to that time, dressed as a pirate, in order to obstruct the scientific development of the USA by making them stick with those unrefined imperial units. $\endgroup$
    – pschill
    Commented Oct 16, 2018 at 11:18

Had the Metric Conversion Act of 1975 been drafted differently, with concrete milestones and requirements, and an intent not just of adoption of metric units, but adoption of existing international standards based on metric, it might well have been the turning point. Having lived through that period, I believe the most significant factor was that it treated treat metric conversion by adopting of dual units, rather than wholesale adoption of related international standards. But it would have required substantially more work and change in the short term than seems to have been politically acceptable.

But instead of mandating a schedule for use of international standards in interstate commerce, it was organized as a voluntary effort, and administered without much urgency.

U.S. Government agencies did make efforts to comply, e.g. contracts after 1976 were written in metric units. But rather than adopting standardized ISO paper sizes such as A4, it continued to order it's traditional paper, by converting inch sizes to fractional metric (e.g. government-letter size was then 203.2 mm × 266.7 mm). This approach seemed to make metric seem harder than it might have otherwise been.

Metrification required more than precise numerical conversions. Changing to new standards which utilized rounded values was more successful, such as the now ubiquitous 2-liter soft-drink bottle. By 1983, (less than 10 years later) metric standards were still not widely used in everyday life, and two American journalists have been commonly cited as the force behind ending the efforts of the metric conversion board.

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    $\begingroup$ So, who are those two journalists commonly cited as the force behind ending the efforts of the metric conversion board ? $\endgroup$ Commented Oct 15, 2018 at 5:47
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    $\begingroup$ According to a March 26, 2006 Washington Post article by Frank Mankiewicz, he and Lyn Nofziger were contributors to the political decision to end further metricification efforts. Nofziger was at the time a political advisor to President Regan. $\endgroup$ Commented Oct 15, 2018 at 19:23
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    $\begingroup$ The Conversion Act was much too late. By 1975, there was a huge install base of non-metric stuff: everything from screw threads to windows to highway mileposts. Sure, a more forceful implementation of the act might result in packaging using metric numbers, but unless you can mandate a complete rebuilding of the entire country, people will still be purchasing two-by-fours to repair their house, shipping goods in twenty-foot containers, and drinking beer by the pint. You note this when you mention paper, but you miss the reason: every filing cabinet and folder is designed for 8.5x11, not A4. $\endgroup$
    – Mark
    Commented Oct 15, 2018 at 22:01
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    $\begingroup$ No doubt, earlier might have been better, but the UK, which initiated metrification only 10 years earlier, has for the most part met with success. $\endgroup$ Commented Oct 15, 2018 at 22:19
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    $\begingroup$ *kilometerstones $\endgroup$ Commented Oct 17, 2018 at 13:08

I know too little of the internal US affairs, but let's take a wide swing.

Help Napoleon

A paramount thing in making Napoleon I lose the war was the attack on Russia 1812 that eventually lead to the first defeat of Napoleon's forces by the allied forces. Notice UK being part of the coalition. Some time before, however, Napoleon was seeking alliance with Russia and was obsessed with attack or at least a blockade of the United Kingdom.

So, open options are:

  • Derail the the Britain-Russian alliance in the context of the Third Coalition (1805).
  • Change the outcome of Trafalgar (1805).
  • There was some kind of a Franko-Russian alliance in 1807 in the context of failed Middle East alliances.
  • There were (two in fact!) marriage proposals from Napoleon to closer Tsar's relatives, 1808 and 1810, if my memory suits me right. Although there was some kind of economical discrepancy, following a peace treaty that was not-so-profitable for Russian trade, it's nothing that cannot be fixed.

Basically, the goal here is either never let Napoleon invade Russia or to split UK from the (historically) winning coalition or to make France invade Britain earlier and/or more successful.

The question was about SI though

What does all this has to do with SI?

Well, SI was invented in France and France was its biggest proponent for quite some time. Taking UK out of political equation would result in much less cultural influence on the USA. Arguably, much fewer Irish people would move to US. But most importantly, the USA-France connection, that was quite warm at the foundation of the USA, would persist and be much, much stronger.

Those new United States might end speaking French or been swallowed up by Canada or what not. They might even not expand to the full size of the our realm's US or do it slower. (I doubt the French Empire would have too much interest in California, but who knows for sure?)

As one of the hallmarks of French cultural and technical expansion to the US, wide adoption of the SI would surely follow.

The aftermath

After the time-traveller returns back to his time, he'd notice severe differences in the US life. Cities might be named differently, have kept their "non-British" designations or not even exist. (Say, NY is New-Amsterdam.) Currency might be called differently and for sure have different design and different people on it. People talk French or at least have much more French than Latin or UK English loanwords in their language. And yes, the flight levels are stated in meters world-wide.

Mission accomplished.

  • $\begingroup$ Exactly! The singular most effective way to guarantee this is by arranging for what we now call the United States to have been subjugated by some ultramarine power who then imposes upon the docile denizens of their newly conquered demesnes their own weird words and fremd figures. We’ve known how super-effective that particular strategy is at this for quite a long time now — ever since 1066 ᴀᴅ or so by my own reckoning. Sure, there’s bound to be some lingering resentment to ausländischen laws governing what you can do with your own language, but that wears off after a chiliad or two. $\endgroup$
    – tchrist
    Commented Oct 17, 2018 at 0:34
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    $\begingroup$ @tchrist This isn't about conquest, but about cultural influence. France was supporting freshly formed USA to subvert British power, had Britain been weakened enough, France could have formed strong and long lasting alliance with USA, which would have resulted in strong cultural influence over country still in formative years, significantly changing entire cultural identity of USA. New country will copy ideas from somewhere out of necessity. Even mild versions of this scenario result in USA having completely different (better BTW) legal system, for example. $\endgroup$
    – M i ech
    Commented Oct 17, 2018 at 9:10
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    $\begingroup$ I was just about to suggest this exact thing. See, the Louisiana Purchase was around this time. What went on with the Louisiana Purchase? Napoleon needed money, so he sold us Louisiana. However he never intended to let us keep it. He always planned on getting it back after mopping up in Europe; he was in trouble at the moment, but giving him the money would allow him to pull through the trouble spot and hed be unstoppable, letting him get it back at his leisure. Or so he planned. $\endgroup$
    – Ton Day
    Commented Oct 18, 2018 at 7:47
  • $\begingroup$ (Dunno what happened, tab crashed and was still editing my accidentally-submitted comment, now I can't edit it any more). So your time traveller helps Napoleon win. You can decide what the effects of such a wild divergence would be in terms of what's convenient or interesting for your story. The least disruptive would be that his downfall is only delayed a short time, so France conquers the US just long enough to change us all to metric and maybe a few other minor tweaks, but can't hold it. $\endgroup$
    – Ton Day
    Commented Oct 18, 2018 at 7:55
  • $\begingroup$ wouldn't it be easier to help the French win the Seven-years-war (en.wikipedia.org/wiki/Seven_Years%27_War)? $\endgroup$
    – chris
    Commented Sep 16, 2020 at 8:15

Travel back to the early Roman Empire and start producing thermometers calibrated to Celsius, precise maps using your knowledge of geometry, precise clocks, scales and kilogram blocks.

Explain how good it will be if the Romans used a standardised system across their empire and encouraged their trade partners to do the same.

Maybe predict a few events to convince them of your brilliance.

By the time Fahrenheit is born nobody cares about his new way to measure temperature. Imperial measurements never existed and the US would have no choice.

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    $\begingroup$ While cool approach, are we sure that it produces USA? What if this change will also cause Roman empire to never fall apart? $\endgroup$ Commented Oct 15, 2018 at 8:44
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    $\begingroup$ I doubt it would even create a metric system. Metric units are nice for a literate, numerate society with widespread access to written works and the need to do math in a base-10 system against quantities fairly frequently. For other uses, we deal with it because it's handy that we all have a common vocabulary. Customary units are handy for normal household use cases. We'd probably end up with the metric system getting supplanted by the Arabic system again, never to return. $\endgroup$
    – Alex H.
    Commented Oct 15, 2018 at 16:09
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    $\begingroup$ The Roman's (and other ancient peoples) weren't stupid or obstinate. They didn't standardize measurements across the empire because it was A) very difficult and B) not that useful at the time. If this were to be attempted, you'd find an audience more unwilling to change than the Americans we already have. $\endgroup$
    – user458
    Commented Oct 15, 2018 at 21:09
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    $\begingroup$ It's an interesting idea, but I had to downvote because the chief advantage of the metric system is nice easy multiples of ten everywhere. But this only matters if you use Arabic numerals to do your arithmetic. The Romans used Roman numerals, which are much clunkier. Base 10 doesn't really help much. And if you give the Romans Arabic numerals, that can change a lot. Ancient mathematicians came close to inventing, say, calculus. The consensus is with a better number system they might have done it. Inventing physics hundreds of years before Newton would snowball entirely unpredictably. $\endgroup$
    – Ton Day
    Commented Oct 18, 2018 at 8:03
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    $\begingroup$ So, instead of being a nice, sensible 5 foot 8 inches I'd be CLXXII cm tall? $\endgroup$ Commented Oct 18, 2018 at 19:00

Well, since you're already familiar with Hitler in your time travels, and Germany had been using the metric system since about 1870, the answer practically presents itself:

Help Hitler win WWII, and occupy the USA too

(Optionally, kill Hitler afterwards, just a little later than the first time)

I think the USA would still be called something very similar to "USA" (since I think occupied France was still called something like "Military Administration in France" (German: Militärverwaltung in Frankreich; French: Occupation de la France par l'Allemagne))

And it shouldn't be impossible to do, there's lots of ideas on how he could have won, but besides convincing him to change a bunch of strategies, maybe just go straight to having him research nukes first... maybe by convincing Hitler than scientists (specifically nuclear) are his only chance.

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    $\begingroup$ Since the asker already mentioned Hitler this was the first thing that occurred to me. I'm sure the American Reich would use metric. No need to persuade people about nuclear weapons, just get all the available Manhattan Project documentation in a nice binder and drop that off in Germany around 1940. Also tell Hitler to have armed guards with him at all times in April 1945 to kill an armed assassin who appears out of nowhere. $\endgroup$
    – Eric Nolan
    Commented Oct 16, 2018 at 9:53
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    $\begingroup$ It would take a pretty drastic change to get Hitler to win World War II, especially if you want him to occupy the USA, rather than just fight to a standstill. $\endgroup$
    – Mark
    Commented Oct 16, 2018 at 19:49
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    $\begingroup$ A further issue is that quite some of the fleeing scientists were Jewish. If the third Reich really would like those people to build them an A-bomb, how about no Kristallnacht and no Auschwitz? Which would rather change The Nazis, up to being arguably impossible. $\endgroup$ Commented Oct 17, 2018 at 15:56
  • $\begingroup$ @OlegLobachev very true... Being a little more liberal with the question's premise ("I am able to convince up to ten people") maybe they could convince Hitler et al. to be a little nicer, maybe help found Israel instead of those camps (I don't know all the historical details, but it seems crazy they didn't do that in the first place, maybe they were just insane). $\endgroup$
    – Xen2050
    Commented Oct 18, 2018 at 1:09
  • $\begingroup$ @Xen2050: First discriminating nazi laws were passed in 1935, if I recall correctly. $\endgroup$ Commented Oct 18, 2018 at 19:39

Remember the Mars probe that was lost because someone forgot to switch between metric and non-metric? Infiltrate NASA and cause the first moon mission to fail because of that. Even better, have the rocket explode in a populated area.

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    $\begingroup$ and back to customary units they go...... $\endgroup$
    – KalleMP
    Commented Oct 15, 2018 at 7:48
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    $\begingroup$ I think that would push us to stop allowing anyone to use SI units before it would do the other thing. $\endgroup$
    – workerjoe
    Commented Oct 15, 2018 at 17:21
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    $\begingroup$ NASA actually did use SI units even before that, it was Lockheed Martin that messed up. $\endgroup$
    – ventsyv
    Commented Oct 15, 2018 at 21:11
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    $\begingroup$ @ventsyv The entire US aerospace industry is inch-pound-seconds, and to a large extent the world, i.e. Airbus uses inch hardware so their structures are largely soft metric. The issue wasn't units, but rather a failure to validate against the interface control document. There are many more things to screw up between organizations, such as which direction is "up" on a vehicle. $\endgroup$
    – user71659
    Commented Oct 15, 2018 at 23:43

Put it in the Bible.

Travel back to the aftermath of Christ's death, before the apostles spread out. Present yourself to the apostles as a prophet/emissary.

Do a couple miracles to establish yourself, using modern technology which should be indistinguishable from magic.

Then present your revelation. Distribute printouts. At least a couple of them will write it down in their gospels.

(There's twelve of them, but not all will go on to write gospels. Convincing ten is more than enough)

The revelation includes the units of measurement to be used by God's people:

  • The Celsius scale. Fresh water at sea level freezes at 0ºC, and boils at 100ºC.

  • The meter. 1/Nth of the distance between specific features of two monuments which survived to the modern age. E.g. the door of a temple, the vomitorium in the Coliseum, the central pillar(s?) in the Pathernon's facade. If you can give them two familiar monuments that's better, if you can score a round number that's best. But an arbitrary number and faraway cities will work just fine, tell them it's "about the length of a step of a man" and give out meter-long staffs to kick-start rough use, later scholars will refine it.

  • The liter. The volume of a cube a tenth of a meter on all sides. Give out liter containers.

  • The Kilogram. The mass of a liter of water (distinguishing mass from weight to ancient fishermen may be hopeless, so you might want to go with the "weight" of a liter of water). Give out 1kg weights.

  • The standard multipliers. Kilo, mili, micro, the whole thing.

  • The second. The time it takes a 1kg sphere of pure iron to hit the ground when dropped from X meters. Hours and minutes defined relative to seconds. (Are you sure you do not want to use one of those nerdy alternative 10-based time scales instead? Whatever.) Give out minute-long and hour-long hourglasses.

Note that this is far too much information to hold in their heads, so the printouts are important.

No way early Americans will ignore the units mandated in the Bible. I don't know anything about the history of imperial units, but they may be pre-empted altogeter since the British were Cristians since before the Empire.

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    $\begingroup$ The apostles explicitly argued against this level of legalism in the Bible. What in the heck does a specific set of units have to do with Christ changing your heart so you can be a better person? I'm pretty sure you'd just be rejected as a false prophet. ...Convincing the Roman Catholic Church before the Reformation might work, though. $\endgroup$
    – jpmc26
    Commented Oct 18, 2018 at 19:55
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    $\begingroup$ If this would work, why aren't we using Cubits, Ephahs, and Shekels? $\endgroup$
    – Michael J.
    Commented Oct 18, 2018 at 23:01
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    $\begingroup$ As an English chap once told me, "If the good Lord had intended us to use the metric system, he would've had ten apostles!" $\endgroup$
    – Kyralessa
    Commented Oct 19, 2018 at 10:58
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    $\begingroup$ @DougR. No, the reason for going after the Church prior to the Reformation is that the units would become customary since the Church was more willing to impose requirements on behavior. While Luther might argue against requiring its usage, I doubt he'd suggest everyone needs to switch to something else. In hindsight, though, a better bet might be to go after the actual Roman Empire and/or subsequent governments. $\endgroup$
    – jpmc26
    Commented Oct 19, 2018 at 18:25
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    $\begingroup$ "Verily I say unto you, even a large step of the Son of man will be as much as the light of the sun itself will have travlled while some 9.147 billion times the tiniest speckle of Caesium hath jumped to and fro between its hyperfine structure levels" - by the way, the next time travel excursion should turn billions into milliards ... $\endgroup$ Commented Oct 21, 2018 at 22:41

To quote the accepted answer:

In 1793, Thomas Jefferson ordered a set of instruments from France that would let the US calibrate to SI units, but the ship hit a storm at sea, blowing his ship into the Caribbean. There it was attacked by pirates (British privateers). The materials never arrived. By the time France sent a second set, US had a new Secretary of State who didn’t like metric system.

That Secretary of State was Edmund Randolph. Remove him from the equation (assassination is probably easiest) just before he's appointed to his new position in 1793, and Jefferson (his predecessor) would most likely remain on in the position, or at least have enough of an influence to ensure that the second set of metric instruments would be adopted.

Note that Randolph did accomplish some quite noteworthy things before his appointment as Secretary of State, hence his death should only be scheduled to occur after those. As noted, just before his appointment would be safest.



I misread the OP's question and didn't realize he was looking for an historical event. I apologize. This isn't an answer to his question. But I had a lot of fun writing it, so I'm going to leave it up. Please don't vote for it. Cheers.

Not that I can believe (as an American)

In reality, the issue is cost. It's the consequence of a capitalistic society combined with a representative government.

Senator: We need to stop using multiple systems of measurement!

People: OK, we can see the value in that...

Senator: It means changing our schools and businesses! Everything from the paper we use to the measuring cups in our kitchen drawers! Think of the jobs! Think of the opportunity!

People: Wait, my measuring cups? Do you even know what dry measure is in the metric system? My paper? Who's going to pay for all this?

Senator: We'll need to pass a temporary tax to help subsidize business and schools to affect the change!

People: There hasn't been a temporary tax in U.S. history!1 I'm not voting for that! Government hasn't used a dollar efficiently since day one! Heck no, we won't go!

And after the protests have died down, we're back at square one.

We've had the same problem with adopting credit card security measures in use in Europe for years and years — the cost to convert everybody is whomping enormous, no one's willing to pay the price, and no one's willing to vote for anybody who's willing to committ to deficit spending to make it happen. The credit card industry finally forced the issue by making businesses responsible for fraudulent spending if they didn't change — and two years later there are a lot of businesses that still haven't changed.

Has there ever been examples of this happening successfully? Oddly, there are (kinda). The Feds outlawed the manufacture (and eventual sale) of 40W, 60W, 75W, and 100W incandescent light bulbs (a lovely attempt by the environmentalists to force the citizenry to reduce their power bills. You'd be surprised what we fight against). It happened — and while some people cheered, many loathed it.

It also happened with the conversion of TV broadcasting from analog to digital. The only way it happened was by the Feds giving away free analog-to-digital conversion boxes.

But converting the way we measure things?

In the end, people don't care about light bulbs so long as they fit in the lamp and do their job. Kinda ditto with TV. You don't actually need to think about anything (and Americans as a people aren't the best thinkers, not since WWII anyway). On the other hand, swaping out all our rulers, scales, forcing us to think about carrots in terms of grams.... (Although it has worked for soda. That's a curiosity all by itself....)

So, despite our entire scientific community using SI units, and pretty much all our cars using metric nuts and bolts, I honestly can't see any way to force such a change on the people other than the government simply choosing to do it — and whichever political party is in power at that time can expect to loose the presidency for 8-16 years because people will absolutely howl. Suddenly all of their great-grandma's recipies don't work anymore.


Unless the government simply chose to mandate that all labeling of all products had to be metric-only. After that it would take (literally) 100 years to get everyone on board, but it would eventually happen. I think. (Oh, people would howl.)

Yeah. We're funny people.

1Whether there has or hasn't isn't relevant. We don't perceive that there ever has been one. It's a very personal thing.

  • $\begingroup$ You're not the only ones: spectator.co.uk/2016/07/… $\endgroup$
    – nzaman
    Commented Oct 14, 2018 at 16:31
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    $\begingroup$ "Suddenly all of their great-grandma's recipes don't work anymore." we often have that problem here in NZ, my grandparents all grew up with imperial units, either here or in England, and all the old recipes in family cookbooks now have to have conversions in the margins and a lot of those conversions are a bit rough on the final result. $\endgroup$
    – Ash
    Commented Oct 14, 2018 at 17:20
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    $\begingroup$ @ShawnV.Wilson, it really is - and I suspect the Auto industry will lead the way. It's so common today to need a full set of Metric wrenches to work on your Ford automobile (the absolute epitome of American automobiles) that it's inevitable. But... I worked in a hardware store for some years, and it was amazing how often people would bring in their Ikea instructions looking for an 8M screw and having no idea what they were looking for. (On the other hand, I laughed everytime someone brought in instructions for metric wood screws - as if the wood would care.) $\endgroup$
    – JBH
    Commented Oct 14, 2018 at 18:00
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    $\begingroup$ @ShawnV.Wilson Nobody really measures soda though (it also helps that 2 liters is close to two quarts). A 2-liter soda bottle might as well be a unit quantity of its own. You buy it, you pour a glassful (however big your cups happen to be), you drink that, and you buy some more when you're running out. Smaller volumes of soda don't even use the same units; we measure bottles and cans and cups/glasses and rum and cokes in ounces. People are comfortable with liters of soda because they don't measure or divide them. $\endgroup$ Commented Oct 14, 2018 at 21:53
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    $\begingroup$ I think it is important to know that since 1812 (when we fought another country that used feet and pounds instead of metric) America’s success in winning wars has been inversely proportional to its military’s use of metric. $\endgroup$
    – Readin
    Commented Oct 16, 2018 at 23:38

Even though the website which displayed recent (1990s) plans for an invasion has disappeared, you could go further back to 1927 and convince Canada to follow through with its invasion plans - and win.
Advantage: we all use the metric system.
Disadvantage: poutine, DunkinDonuts never exists as TimHorton's covers the continent.


Convince the Warren court that it is a moral imperative for the country to adopt metric. You bypass potential political objections, you only have to convince 5 people. For extra assurance you can convince the other 4 justices plus the president.

The SC will rule all other measurement systems unconstitutional and the president will enforce the change.

You accomplish the change with minimal impact in everything else and you make the change late enough that the use of an inferior system doesn’t cause America to lose any major wars.

  • $\begingroup$ You overestimate the power of the Supreme Court. In the words of Andrew Jackson: "[He] has made his decision; now let him enforce it.". If the court makes a decision that is sufficiently in opposition to what people will accept, it will simply be ignored. $\endgroup$
    – Mark
    Commented Oct 16, 2018 at 19:46
  • $\begingroup$ @Mark That was a long time ago. In the modern era enforcement hasn’t been an issue. But as I said, if you want added assurance you can also convince the president because under the terms of the question you can convince up to 10 people. If you are still doubtful you can remember that you only need five justices for a majority so you can convince just 7 justices, 1 president, 1 House speaker and 1 Senate majority leader. Drop the number of justices to five and you can add Walter Cronkite and Johnny Carson to your list so that public opinion can be swayed. $\endgroup$
    – Readin
    Commented Oct 16, 2018 at 21:08
  • $\begingroup$ Looking at the politics of the era, you'd be better off convincing Eisenhower that metrication is a matter of national defense than convincing Warren that it's a moral imperative. The Warren court was a leader in individual liberties, which doesn't really translate well into forced adoption of the metric system. I still don't think it would work, though. $\endgroup$
    – Mark
    Commented Oct 16, 2018 at 21:26
  • $\begingroup$ @Mark Even if Eisenhower thought metric were necessary for national defense he still would have gone though Congress and then you would need to convince a couple hundred people instead of just 10. The key thing with Warren was his willingness to use his office to effect changes despite the limitations of his office. If the law didn’t say what he wished it did then he simply made something up. $\endgroup$
    – Readin
    Commented Oct 16, 2018 at 23:32

I would talk to whoever is in charge of the US at the time of the invention of the metric system and tell them to adopt them as a way to show patriotism: "imperial units are from those nasty Brits, we want none of that!"

Calls to patriotism are the easiest way to get anyone to do anything, beside perhaps, calls to faith.

  • $\begingroup$ that would not work $\endgroup$
    – Topcode
    Commented Sep 14, 2020 at 22:43
  • $\begingroup$ This is a lot more doable than you think. market an idea right, and you can get it done. In the US, patriotism would be a good horse to ride on. $\endgroup$
    – chris
    Commented Sep 16, 2020 at 8:19

Torpedo the Mayflower

You would have to literally wipe out every American and eradicate all of our history to get us to adopt the French Revolutionary "SI" system of measurement. We will fight to the last man, fight on the beaches, fight in the hills, fight in the forests, etc, etc,...

If you could take a submarine with you and simply torpedo every ship carrying English colonists for a few centuries, leaving the French to settle North America, then you might pull it off. Good luck, ami.

  • 7
    $\begingroup$ Are you joking? Because lots of Americans want the metric system, it's just not a big majority. $\endgroup$
    – Caleb707
    Commented Oct 15, 2018 at 20:02
  • 1
    $\begingroup$ I wouldn't say joking exactly, but it was somewhat of a lighthearted take. But don't you come for my rulers and tape measures. $\endgroup$
    – workerjoe
    Commented Oct 15, 2018 at 20:36
  • 1
    $\begingroup$ Yeah! Murica! We'll fight by the pound, mile, and gallon. $\endgroup$
    – user458
    Commented Oct 15, 2018 at 21:26
  • 10
    $\begingroup$ My 9mm is locked and loaded... oh wait $\endgroup$
    – workerjoe
    Commented Oct 16, 2018 at 1:37
  • $\begingroup$ This is a bad idea... but just a detail about needing a torpedo or a whole submarine to eliminate the Mayflower? It's a wooden ship, all you need is a match, or a lit cigarette in the right place at the right time $\endgroup$
    – Xen2050
    Commented Oct 16, 2018 at 6:57

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