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What if all the water in the oceans suddenly froze? How much of the landmass will be covered in ice?

That is a fascinating “what if” scenario. You’ve hit on one of the most unique properties of water: anomalous expansion. While almost every other substance shrinks and becomes denser as it turns from a liquid to a solid, water decides to be different.

Because of the way hydrogen bonds form a hexagonal crystalline lattice when freezing, ice ends up being about 9% less dense than liquid water.

Here is what would happen if we hit the “freeze” button on all the Earth’s water.

1. The Volume Increase

To figure out the scale of this, we have to look at the total volume of water on Earth. There are approximately 1.386 billion cubic kilometers ($1.386 \times 10^9 \text{ km}^3$) of water on our planet.

If all of that liquid water turned into ice:

The Math: $1.386 \text{ billion km}^3 \times 1.09 \approx 1.511 \text{ billion km}^3$.
The Result: We would suddenly have an extra 125 million cubic kilometers of “stuff” on the surface. To put that in perspective, that extra volume alone is enough to cover the entire United States in a layer of ice about 13 kilometers (8 miles) thick.

2. Would it cover the entire surface?

The short answer is no, but it would come surprisingly close to reclaiming a lot of land.

The oceans have an average depth of about 3.7 kilometers (12,100 feet). If that entire column of water froze and expanded upward:

Vertical Rise: A 9% expansion of 3.7 km is roughly 333 meters (about 1,092 feet).
The Coastal Impact: A 333-meter rise in the “sea level” (now the ice level) would submerge almost every major coastal city on Earth. New York, London, Tokyo, and even higher-altitude spots like Paris would be buried under the expanding ice shelf.

However, the average elevation of land is about 840 meters above sea level. Since the highest points (like the Himalayas or the Andes) reach nearly 9,000 meters, a 333-meter expansion isn’t nearly enough to cover the entire globe. Huge portions of the interior continents would remain “dry”—though they would be incredibly cold.

3. The “Snowball Earth” Effect

While the expansion of the liquid water wouldn’t cover the mountains, the climatic transition would.

Albedo Flip: Ice is highly reflective. Currently, the oceans absorb most of the sun’s heat. If they turned into a white sheet of ice, they would reflect about 80% of the sun’s energy back into space.
Atmospheric Freezing: If the oceans are frozen, the water cycle stops. No evaporation means no rain. The remaining moisture in the atmosphere would fall as snow and never melt, eventually covering the remaining land in a permanent white shroud.

Summary Table: Liquid vs. Ice

Metric	Liquid Water (Current)	Frozen Water (Post-Expansion)
Total Volume	$\approx 1.386 \text{ billion km}^3$	$\approx 1.511 \text{ billion km}^3$
Average Ocean Depth	$\approx 3.7 \text{ km}$	$\approx 4.03 \text{ km}$
Surface Coverage	$\approx 71\%$	$\approx 80-85\% \text{ (due to low-land flooding)}$

It’s lucky for us that the “anomalous” part of water’s expansion happens the way it does. If ice were denser than water, it would sink to the bottom of the ocean, the sun would never reach it to melt it, and our oceans would have frozen solid from the bottom up billions of years ago!