In short: water expands by about 9% in volume when it freezes into ice — a US gallon of liquid water becomes about 1.09 gallons of ice, an increase of roughly 0.09 gallons (343 mL). Enter your own volume above for the exact figure, and add a headspace value to check overflow risk in a sealed container.
This is a planning aid based on published density data. For structural, plumbing or safety-critical situations, consult a licensed engineer or plumber.
How to calculate water's freezing expansion
When water freezes, its mass doesn't change — the same molecules simply lock into a less tightly packed solid, so the same mass now takes up more space. That means the whole calculation comes down to comparing two densities:
This calculator computes the density of liquid water at 0 °C with the same Kell equation used on the density calculator, divides it by the ice density you supply, and multiplies that ratio by your volume to get the new, frozen volume.
Worked example. Take 2 liters of water. The expansion factor is 999.84 ÷ 916.7 ≈ 1.0907. Multiply: 2 L × 1.0907 = 2.181 L of ice — an increase of about 181 mL, which is roughly enough to overflow a completely full, sealed 2-liter bottle.
Weight doesn't change — only volume does. The mass of your water is identical before and after freezing, so if you want the actual weight of that water or ice, use the water weight calculator. What grows here is purely the space it occupies.
Why water expands when it freezes
Most liquids contract as they solidify, because molecules pack more tightly once they stop moving past each other freely. Water does the opposite. As it cools toward 0 °C, hydrogen bonds pull its molecules into an open, hexagonal lattice — the structure behind every snowflake's six-fold symmetry — and that lattice holds the molecules farther apart, on average, than they were in the liquid.
The result is a solid that is about 8–9% less dense than the liquid it froze from, which is also why ice floats instead of sinking. This is an anomaly among common substances: it's one reason lakes and rivers freeze from the top down, insulating the water below and letting aquatic life survive the winter. See the density-by-temperature calculator to explore how density behaves on the liquid side of that same transition.
Freezing expansion of common volumes
Every original volume expands by the same ~9.07% factor (using the default 916.7 kg/m³ ice density), so the increase always scales proportionally. These figures use that default.
| Original volume | New volume as ice | Volume increase |
|---|---|---|
| 1 US cup (0.237 L) | 1.091 cups (0.258 L) | 0.091 cup (21.5 mL) |
| 1 US pint (0.473 L) | 1.091 pt (0.516 L) | 0.091 pt (42.9 mL) |
| 1 US quart (0.946 L) | 1.091 qt (1.032 L) | 0.091 qt (85.8 mL) |
| 1 liter | 1.091 L | 0.091 L (90.7 mL) |
| 1 US gallon (3.785 L) | 1.091 gal (4.129 L) | 0.091 gal (343 mL) |
| 55-gallon drum (208 L) | ≈60.0 gal (227 L) | ≈5.0 gal (18.9 L) |
Worked examples
A full, sealed 500 mL water bottle
+45.3 mL
A 500 mL bottle filled all the way and sealed will try to grow to about 545 mL as ice, with no room to expand. Expect a bulging bottle or a split seam rather than a clean overflow.
A capped 1-gallon jug, full to the top
+11.6 fl oz
One US gallon expands to about 1.091 gallons — an increase of roughly 11.6 fl oz. Left with no headspace, that pressure is enough to crack a rigid plastic jug.
Trapped water in a garden-hose fitting
+2.3 fl oz
Even a small trapped volume — about 0.2 gallons in a hose or fitting — grows by roughly 2.3 fl oz when it freezes solid. That small increase is routinely enough to split copper or brass fittings.
What else affects the result
Trapped air in the ice. Freezer ice is rarely perfectly clear. Air bubbles lower its effective density to around 900 kg/m³, which very slightly increases the expansion percentage — use the advanced ice-density field above to model this.
Dissolved salts and impurities. Seawater and brine don't freeze as a single solid at 0 °C; pure ice crystals form first and push dissolved salt into pockets of liquid brine, so the freezing point keeps dropping as freezing progresses. This calculator models fresh, salt-free water.
Confinement, not just percentage. A 9% increase is a small fraction of most containers, but water and ice barely compress. In a sealed, rigid container the same small volume change turns into very high internal pressure — that's what actually cracks pipes and bottles, not the raw percentage.
Rate of freezing. Slow, gradual freezing tends to produce clearer, denser ice with fewer trapped bubbles than a fast freeze, which is one more reason real-world results vary slightly from the laboratory ice-density figure.
Frequently asked questions
How much does water expand when it freezes?
Water expands by about 9% in volume when it freezes into ice, using a typical ice density of 916.7 kg/m³. A US gallon of water becomes about 1.09 gallons of ice — an increase of roughly 0.09 gallons, or about 343 mL for a full gallon.
Why does water expand instead of contract when it freezes?
Almost every liquid contracts as it solidifies, but water is unusual. As it cools toward 0 °C, its molecules lock into an open hexagonal lattice held apart by hydrogen bonds, which takes up more space than the same molecules moving freely as a liquid. The result is a solid that is less dense than the liquid it came from, which is also why ice floats.
Can freezing water really crack a pipe or a full water bottle?
Yes. A 9% volume increase sounds small, but water and ice are both nearly incompressible, so a sealed, rigid container with no room to expand converts that small volume change into very high internal pressure rather than a gentle bulge. That pressure is enough to split copper and PVC pipe, crack glass bottles, and warp plastic containers.
Does saltwater expand the same amount when it freezes?
The ice itself expands by a similar percentage, but seawater does not freeze as a single solid block at 0 °C. As it cools, mostly pure ice crystals form first and dissolved salt is pushed out into pockets of concentrated brine, so the freezing point keeps dropping and only part of the volume solidifies at any given temperature. This calculator models freezing of fresh, salt-free water.
Does the ice keep expanding the colder my freezer gets?
No — almost all of the expansion happens right at the freezing transition, when liquid water becomes solid ice. Once it is fully frozen, further cooling actually causes the solid ice to contract very slightly, the opposite of the freezing expansion, and the effect is far smaller than the initial 9%.
Why does the calculator let me change the ice density?
Freezer ice is rarely perfectly bubble-free. Trapped air can lower its density to around 900 kg/m³, which increases the expansion percentage slightly, while slow-frozen, dense ice can approach the 916.7 kg/m³ reference value. Adjusting the ice density lets you match the calculator to real-world ice rather than the laboratory ideal.
Sources & references
- Kell, G. S. (1975). Density, thermal expansivity, and compressibility of liquid water from 0° to 150 °C. Journal of Chemical & Engineering Data, 20(1), 97–105.
- Petrenko, V. F., & Whitworth, R. W. (1999). The Physics of Ice. Oxford University Press.
- National Institute of Standards and Technology (NIST). Thermophysical Properties of Fluid Systems.
John Mac, PE
Water Systems Specialist · Austin, Texas
Texas-licensed Professional Engineer with 13+ years in residential water systems and 180+ completed projects. Writes and reviews the calculators on watercalculator.us. Read full bio
Texas PE (2016) · BS Civil Engineering, Hydraulics (2013)