I am creating a fantasy world where a given race is mystically tied to the planet. Predominately this race will be earth-dwellers, quite happy and content to burrow underground, but I'd like some of the race to be happier in the sea. The world is very Earth-like, so it works as a good model.

I know that the Earth's surface is covered by 71% water and roughly 10% by ice. And I know the Earth is about 0.023% water by mass, but that's a comparison against the total mass of the Earth. Neither of those figures however are what I'm after; surface area gives too large a percentage and the total percent by mass is probably too low.

So, the question is how much of the Earth's crust water by mass? As in what is the mass of the oceans, seas, rivers, and so on, compared just to the stones and rocks that make up the surface of the planet: the continents, sea-floors, and everything down to the mantle? I'm not even sure I'd know where to begin on that calculation, so even a rough ballpark would be helpful.

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    $\begingroup$ Can you give some idea of how "deep" you want the surface to be considered? $\endgroup$
    – Tim B
    Commented Feb 9, 2015 at 9:32
  • $\begingroup$ How "deep"? No idea off the top of my head, but, while geology knowledge may not be that great, I do believe that as a geological term, the Earth's crust is pretty well defined already. $\endgroup$ Commented Feb 9, 2015 at 23:08
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    $\begingroup$ You know, scientists have discovered that earth has at least three times the amount of water in the ocean in the crust, and that it is in a spongy stone. $\endgroup$ Commented Feb 16, 2016 at 4:50

1 Answer 1


The Earth's crust has a mass of $1.913*10^{22}$ kilograms and its oceans have a mass of $1.35*10^{21}$ kilograms.

If you want to include all the mass from the mantle up to the surface as "the surface of the Earth" then simply add the two together: $2.048*10^{22}$ kilograms of crust and ocean riding on the mantle.

The oceans are about 6.6% of the mass from the mantle to the surface of the Earth.

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    $\begingroup$ note there is a lot of hydrated minerals so the amount of water should be much larger than just toe content of the oceans. $\endgroup$
    – John
    Commented Jan 11, 2022 at 0:39

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