Maximum density of water (4 °C)
| Value | 999.975 kg/m³ |
| Status | Measured: ± 0.001 kg/m³ (0.000001 relative) |
| Source | Tanaka et al. (2001), CIPM-recommended formula for VSMOW |
| Categories | ThermodynamicMaterial Properties |
| microgram per liter | 999,975,000 μg/L |
| milligram per cubic meter | 999,975,000 mg/m³ |
| milligram per liter | 999,975 mg/L |
| pound per cubic yard | 1,685.5128 lb/yd³ |
| kilogram per cubic meter | 999.975 kg/m³ |
| gram per liter | 999.975 g/L |
| pound per cubic foot | 62.4264 lb/ft³ |
| pound per imperial gallon | 10.022162 lb/imp gal |
| pound per US gallon | 8.3451958 lb/gal |
| slug per cubic foot | 1.9402718 slug/ft³ |
| gram per cubic centimeter | 0.999975 g/cm³ |
| gram per milliliter | 0.999975 g/mL |
| kilogram per liter | 0.999975 kg/L |
| tonne per cubic meter | 0.999975 t/m³ |
| US short ton per cubic yard | 0.8427564 ton/yd³ |
| pound per cubic inch | 0.036126389 lb/in³ |
Water at any temperature
0 to 100 °CThe value above is one point on this curve. Liquid water from 0 to 100 °C at 1 atm — density, viscosity, specific heat, thermal conductivity and vapour pressure, all at the same state.
Learning zone
Almost every liquid gets denser as it cools, right down to freezing. Water reverses near 3.98 °C: below that, hydrogen bonds start assembling the open tetrahedral structure of ice, and the liquid expands again. The peak density is 999.975 kg/m³ — the reason the kilogram was originally meant to be the mass of a litre of water, and the reason that definition was so nearly right.
The consequence is ecological. As a lake cools in autumn the surface water sinks until the whole body reaches 4 °C; colder water is then lighter and stays on top, freezing into a floating lid that insulates everything beneath. Lakes freeze from the top down, not the bottom up, and fish survive the winter. Ice itself is 917 kg/m³, about 8 % less dense than liquid water, which is why it floats and why frozen pipes burst.