Scale, geology and a very large quantity of water

How Much Water Would the Noachian Flood Require?

If the Flood is read as a literal global event in which the highest mountains were submerged, the first problem is not zoology or shipbuilding. It is geometry.

Using the modern height of Mount Everest as the minimum target and treating Earth as a sphere, the water needed to raise sea level by 8.849 km is about 4.52 billion cubic kilometres in the layer above present mean sea level.

Earth mean radius 6,371 km NASA reference value

Everest above sea level 8.84886 km official China-Nepal measurement

Present ocean volume 1.335 bn km³ NOAA estimate

1. What does “cover the mountains” mean geometrically?

Genesis 7:19-20 describes the waters as covering “all the high mountains” and then rising further. For a deliberately conservative physical test, we can ignore the additional “fifteen cubits” and ask only how much water is needed to bring a global water surface up to the height of the highest modern mountain.

In reality, 8.849 km is only about 0.14% of Earth’s radius, so a correctly scaled flood layer would be almost invisible in a diagram of the whole planet.

2. The calculation

The volume of a sphere is \( \frac{4\pi r^3}{3} \). The additional layer between present mean sea level and a new global level h kilometres higher is therefore:

V = 4π/3 × [(R + h)³ − R³]
R = 6,371 km
h = 8.84886 km

V ≈ 4,519,760,916 km³

Rounded sensibly, that is 4.52 billion km³ of water occupying the shell above present mean sea level.

Important qualification: real continents and mountains occupy some of that shell, so 4.52 billion km³ is not a topographically exact “extra water” figure. A digital elevation model would reduce it somewhat. It does, however, establish the correct scale: several times the volume of the present oceans.

3. Compare that with all the water in today’s oceans

NOAA gives the volume of the modern oceans as about 1.335 billion km³. The simple flood shell is therefore about 3.39 present ocean volumes.

Present oceans1.335 bn km³

Water shell to Everest height4.520 bn km³

The second bar is the simplified spherical-shell calculation. Land relief would displace a fraction of it, but not enough to alter the order of magnitude.

4. If the water arrived during forty days of rain

Genesis also describes forty days and nights of rain, while separately mentioning the “fountains of the great deep”. If, merely as a scale comparison, the whole 8.849 km rise had to be supplied uniformly during those forty days, the mean accumulation rate would be:

Per day 221 m of water depth every day

Per hour 9.22 m every hour for 960 hours

Per second 2.56 mm each second, everywhere

This is a rate illustration, not a claim that Genesis says rainfall alone supplied the water.

5. Where could the extra water come from — and where could it go?

NOAA, citing USGS, estimates that all water presently on Earth amounts to about 1.386 billion km³. The spherical flood shell alone is more than three times that entire present terrestrial water inventory.

This makes the source-and-disposal problem unavoidable for a literal global interpretation. Water brought from a previously hidden terrestrial reservoir must still fit somewhere within the Earth system before the Flood, while water remaining after the Flood must subsequently be stored somewhere without leaving modern sea level kilometres higher. Invoking the atmosphere does not solve the bookkeeping: the issue is not merely how water circulates, but the total volume that must exist.

The central point is deliberately narrow. This page does not attempt to decide questions of theology, genre or ancient cosmology. It asks only what follows physically if “all the high mountains” is interpreted as a global hydraulic statement about the modern Earth.

6. Try another assumed flood height

Enter any height above present mean sea level. The calculator uses the same spherical-shell model and shows the corresponding volume and forty-day accumulation rate.

Flood level above present sea level, metres

Sources and assumptions

NASA Science — Solar System Sizes: Earth mean radius approximately 6,371 km.
NOAA Ocean Service — How much water is in the ocean?: approximately 1.335 billion km³ in the oceans and 1.386 billion km³ total water on Earth.
Ministry of Foreign Affairs of the People’s Republic of China: joint China-Nepal announcement of Mount Everest/Qomolangma at 8,848.86 m.
Biblical references: Genesis 7:12, 7:19-20. Translation wording varies; the physical calculation here depends only on the global-mountain-covering interpretation.

Model limitations: Earth is treated as a sphere; present mean sea level is used as the reference surface; actual terrain displacement, gravitational redistribution, crustal loading, erosion and geodynamic effects are omitted. These refinements matter to a precise geophysical model, but not to the conclusion that the required volume is measured in several present-ocean volumes.