I'm creating a planet with an Earth-like environment for a sci-fi campaign game. The game is operational/tactical but has some strategic aspects. Specifically, players will only be able to purchase units they can afford. I'd like to base military budgets on each nation's gross national product (GNP). How would I generate the numbers?

I appreciate any help!

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    $\begingroup$ You'll need a basic understanding of each nation's manufacturing needs and products, and the trade between the nations. $\endgroup$
    – Brian Lami
    Jan 12, 2018 at 6:49
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    $\begingroup$ This seems way too broad. You're essentially asking people to invent an entire economic system for you as it stands. $\endgroup$ Jan 12, 2018 at 7:33
  • $\begingroup$ @StephenG No it's not. Just find out how GNP is devised for an economy and apply that to the imaginary nations. If do it by inventing entire economies, then it would be too broad, but it would be silly. $\endgroup$
    – a4android
    Jan 12, 2018 at 7:59
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    $\begingroup$ @a4android We have no idea how the OP has designed the economy for this game. It may have no obvious connection with how real economies operate. We don't even know if the OP has devised an economy for his game. Unless there is come clarification I'd still consider this too broad. $\endgroup$ Jan 12, 2018 at 8:12
  • $\begingroup$ @StephenG It's easier to understand by doing a bit of research into what the concept involves. $\endgroup$
    – a4android
    Jan 12, 2018 at 8:32

6 Answers 6


You don't want to get into specifics

Ultimately, the calculation of gross national product (GNP) is a pretty in-depth measure. Not only do you have to calculate the value of all goods produced, you also would have to calculate the value of all services provided. That means you have to know all the good produced and services provided on your world.

This is harder than it looks. The Bureau of Economic Analysis in the United States identifies 403 separate industries that it analyzes. Do you know what the contribution of copper, nickel, lead, and zinc mining is in our world? Well, make sure you don't confuse it with iron, gold, silver, and other metal ore mining since that is a separate industry. What about the manufacturing of abrasive products, irradiation apparatus manufacturing, carpet and rug mills, news syndicate, lessors of nonfinancial intangible assets, services to building and dwellings, home health care services and religious organizations?

The point is, you don't want to be stuck quantifying all these individual fields to attempt to come to some numerical solution.


I would suggest simply doing research on a current day or past nation, and carry forward the same ratios of expenditure.

For example, if you use the modern day US, a filthy rich player character (PC) might be worth a billion dollars. A brand new aircraft carrier costs 13 billion dollars; not affordable. Meanwhile, an M1 Abrams main battle tank cost the Saudis about $10 million each. So that would be affordable.

Going back in time for a different recommendation, a study of England in 1900 turned up 540 business estates worth an average of 590,000 pounds. So you might estimate a filthy rich PC would be worth that much. Meanwhile, HMS Dreadnought cost 1,785,683 pounds to build; relatively cheaper than an aircraft carrier is today.

If your planetary society is more like the US (more democratic, higher floor for standard of living, low birth/growth rate) or 1900 England (more aristocratic, lower classes in relative squalor, high birth/growth rate), you can choose a set of numbers that suits you. The same method can be applied to basically any other goods or services that you want your PCs to purchase.


Games I’ve seen mostly take one of two approaches. Either,

  1. They assign each city a “revenue” number, possibly scaled according to population, and the size of your economy is the sum of the value of all your cities. This is somewhat realistic because in postindustrial countries (i’m assuming from you saying the game is “sci-fi”), cities are vastly wealthier than rural areas. If you want to make the model slightly more sophisticated, you can multiply the value of your cities by trade between it and the other cities in a country, so a clever player can tank an opponent’s economy by blockading the links between the cities instead of conquering or destroying the cities themselves. However if conquest is something you want to have a lot of in your world, this is probably not the way to go, because physical territory is basically irrelevant here. In the real world, capturing a city is a gruesome and blood-drenched endeavor, and often results in the destruction of much of the prize itself. Scads of resistance movements throughout history have also proven that you don’t need to control cities to maintain a war machine.

  2. They tie the economy to the natural resources in the land (food, coal, oil, steel, etc.) and the economy is basically backed by the physical commodities within a country’s territory. This is hugely unrealistic (otherwise Venezuela would be one of the richest countries in the world!) but it has the upside of being simple for players to understand, and can be somewhat accurate if the main focus of your world is warfare, where the basic resources matter much more relative to higher-level goods than they normally would in a civilian economy.


You could create two classes of citizens: civilians and militaries.

Civilians produce a certain amount of money/gold per time (this can be tailored based on the activity), while militaries spend a certain amount of money/gold per time (again tailored per unit type).


  • Lumberjack produces 1 gold/second
  • Engineer produces 10 gold/second
  • Scout costs 0.5 gold/second
  • Sniper costs 10 gold/second

In this way if you want to support a large army you need to have a large economy (population and activities) behind, without venturing into Economic theories and studies.


You can use the standard formula for calculating GNP as we do on planet Earth.

Gross national product (GNP) is a broad measure of a nation's total economic activity. GNP is the value of all finished goods and services produced in a country in one year by its nationals. How it works (Example):

GNP includes income earned by citizens and companies abroad, but does not include income earned by foreigners within the country.

The figures used to assess GNP include the manufacturing of tangible goods (cars, furniture and agricultural products) and the provision of services (education, healthcare, and business services). GNP does not include the services used to produce manufactured goods because their value is included in the price of the finished product. However, GNP does include depreciation and indirect business taxes like sales tax.

The formula for GNP is:

Consumption + Government Expenditures + Investments + Exports + Foreign Production by U.S. Companies – Domestic Production by Foreign Companies = Gross National Product

GNP can be adjusted to make valid comparisons year-to-year or among countries. For year-to-year comparisons, GNP needs to be adjusted for inflation. For country-to-country comparisons, GNP needs to be stated on a per capita basis (i.e. GNP divided by the population of the country).

Source: GNP

This provides some refined appreciation of the nature of GNP.

Gross national product (GNP) is the market value of all the products and services produced in one year by labor and property supplied by the citizens of a country. Unlike gross domestic product (GDP), which defines production based on the geographical location of production, GNP indicates allocated production based on location of ownership. In fact it calculates income by the location of ownership and residence, and so its name is also the less ambiguous gross national income.

GNP is an economic statistic that is equal to GDP plus any income earned by residents from overseas investments minus income earned within the domestic economy by overseas residents.

GNP does not distinguish between qualitative improvements in the state of the technical arts (e.g., increasing computer processing speeds), and quantitative increases in goods (e.g., number of computers produced), and considers both to be forms of "economic growth".1

When a country's capital or labour resources are employed outside its borders, or when a foreign firm is operating in its territory, GDP and GNP can produce different measures of total output. In 2009 for instance, the United States estimated its GDP at \$14.119 trillion, and its GNP at \$14.265 trillion.2

The term gross national income (GNI) has gradually replaced the Gross national product (GNP) in international statistics.[3][4] While being conceptually identical, the precise calculation method has evolved at the same time as the name change.

Source: GNI

The concept is sufficiently general for the OP to be able to devise a sketches for the economies of the nations in his world.


Create a currency and make sure that you know its value compared to the Dollar. Then, you can determine the nation's size, median income and then use that to calculate its gdp. A poor nation would have a gdppc <20k While a wealthy one might be >100k, and a medium one may be around 35k

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    $\begingroup$ So your answer is that to calculate GDP he needs to calculate the factor which determine GDP? Clever! $\endgroup$
    – L.Dutch
    Jan 12, 2018 at 6:20
  • $\begingroup$ Why would these figures apply on an alien planet? Note that OP said Earth-like, not Earth. $\endgroup$
    – user
    Jan 12, 2018 at 9:37
  • $\begingroup$ Welcome to the site. Please note that the Worldbuilding SE is dedicated to providing detailed answers to specific questions. As is, this answer lacks the expected depth necessary to ensure a novice in the field can understand and effectively make use of the information provided. Barring an edit to clarify the point made here, this may be deleted as inadequate. Feel free to take the tour to get a better understanding of the site. $\endgroup$
    – Frostfyre
    Jan 12, 2018 at 13:16

Thanks guys, I have quite a few ideas. Just to clarify a little bit:

  1. This is indeed a SciFi game, set in an undetermined future date.
  2. There are four countries on the planet who will sometimes cooperate and sometimes squabble.
  3. All combat will be on surface, though the countries will be able to obtain combat support aircraft (atmospheric only). While there will be aircraft on board, I'm going to abstract some of the more esoteric aircraft types. For example, strategic bombing will be abstracted, as a percent loss of production capacity (hence the need for baseline GNPs).
  4. BTW, I should mention, this is going to be done with miniatures. The largest scale battles I anticipate will be battalion level, the smallest will be platoon level.

Again, Thanks for the feedback. Once I've gotten the material together, I'll try to post it.

  • $\begingroup$ Could you edit this into the question, rather than posting it into the answer? It might not get seen here. $\endgroup$
    – F1Krazy
    Jan 16, 2018 at 11:30

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