Density of Water: Values, Temperature Effects, and Key Comparisons
Water is the default reference for density in science and engineering, and 1000 kg/m³ is still the number most people remember first. That value is useful, but only under specific conditions, because water changes density with temperature more than many people expect.
This page gives the exact values, a temperature table, comparisons with ice and sea water, and the physical reason water behaves differently from most liquids. When you need to calculate a real problem, open the liquid density calculator and use the same reference data in a live workflow.
Key values
Water Density: Key Values
kg/m³
998.2 kg/m³
At 20°C (room temperature)
g/cm³
0.9982 g/cm³
At 20°C (room temperature)
lb/ft³
62.32 lb/ft³
At 20°C (room temperature)
Maximum density occurs at 3.98°C: 999.97 kg/m³ (≈ 1.000 g/cm³)
Temperature effect
Density of Water at Different Temperatures
Water does not follow a simple linear density trend. As it cools toward 4°C, density rises, but below that point the hydrogen-bond network starts to open up and the volume expands again. That makes water unusual among liquids and explains why the maximum-density point matters so much.
The curve is non-linear, with 3.98°C as the peak. That single feature affects how lakes stratify, how frozen water expands, and how people estimate water mass in temperature-sensitive applications.
| Temperature | Density | Notes |
|---|---|---|
| 0°C | 999.84 kg/m³ | Liquid water at freezing point |
| 3.98°C | 999.97 kg/m³ | Maximum density |
| 10°C | 999.70 kg/m³ | — |
| 20°C | 998.20 kg/m³ | Standard room temperature |
| 25°C | 997.05 kg/m³ | Common lab reference |
| 40°C | 992.22 kg/m³ | — |
| 60°C | 983.19 kg/m³ | — |
| 80°C | 971.82 kg/m³ | — |
| 100°C | 958.37 kg/m³ | At boiling point (1 atm) |
Ice at 0°C: approximately 917 kg/m³ — about 9% less dense than liquid water.
For a broader reference index, open the density table.
Why it peaks
Why Does Water Reach Maximum Density at 4°C?
Most liquids simply get denser as they cool because molecules slow down and pack closer together. That trend is easy to expect, and it is the rule for water until the temperature gets close to 4°C.
Below that point, hydrogen bonds begin to organize water molecules into a more open hexagonal structure. The structure takes up more space, so density starts to fall even though the liquid is still cooling. For the general definition and formula context, see what is density.
The 4°C point is the balance between two opposing effects: thermal motion pushes molecules apart at higher temperatures, while hydrogen-bond ordering pushes them into a looser arrangement at lower temperatures.
The practical consequence matters in winter. Lakes keep their densest water at the bottom, around 4°C, while colder water and ice remain on top. That is one reason aquatic life can survive through freezing weather.
Water vs ice
Density of Water vs Ice
Liquid water at 0°C has a density of 999.84 kg/m³, while ice at the same temperature is only 917 kg/m³. That difference means ice is about 8.7% less dense than water, so it floats instead of sinking.
That simple density gap shows up in glacier movement, frozen pipes, and the reason people can stand on floating ice. For a deeper look at the solid phase, see the density of ice page when it is available.
| Liquid Water (0°C) | Ice (0°C) | |
|---|---|---|
| Density | 999.84 kg/m³ | 917 kg/m³ |
| g/cm³ | 0.9998 | 0.917 |
| vs water | baseline | floats |
Sea water
Density of Sea Water vs Fresh Water
Sea water averages about 1,025 kg/m³, which is roughly 2.5% denser than fresh water. Dissolved salts add mass without increasing volume by the same amount, so the density rises. For salinity, depth, and buoyancy details, see density of seawater.
That difference changes buoyancy, ship draft, and ballast handling. Ships ride a bit higher in salt water, and submersibles or submarines near an estuary may need to adjust because the water column is not as dense as open-ocean water. The Dead Sea is far more extreme and produces very strong buoyancy.
| Water Type | Density (20°C) | Notes |
|---|---|---|
| Distilled water | 998.2 kg/m³ | Pure reference |
| Fresh water | ~998 kg/m³ | Typical river/lake |
| Sea water | ~1,025 kg/m³ | Average ocean salinity 3.5% |
| Dead Sea | ~1,240 kg/m³ | Extreme salinity ~34% |
FAQ
Frequently Asked Questions
What is the density of water in kg/m³?
Pure water at 20°C has a density of 998.2 kg/m³. The commonly cited 1000 kg/m³ is a rounded approximation that is most accurate near 4°C, where water reaches its maximum density of 999.97 kg/m³.
What is the density of water in g/cm³?
At 20°C, the density of water is 0.9982 g/cm³. At its maximum density point of 3.98°C, it is 0.99997 g/cm³, which is why 1 g/cm³ is used as the standard rounded reference value in chemistry.
Why is the density of ice lower than water?
When water freezes, hydrogen bonds arrange water molecules into a hexagonal crystal lattice that takes up more space than liquid water. The same mass occupying more volume means lower density — about 917 kg/m³ for ice versus 999.84 kg/m³ for liquid water at 0°C.
Does salt water have a higher density than fresh water?
Yes. Sea water averages about 1,025 kg/m³ because dissolved salts add mass without a proportional increase in volume. The Dead Sea, with extreme salinity, reaches around 1,240 kg/m³, which is why objects float so easily in it.