Water Density by Temperature

Specific Gravity of Water

Specific gravity (SG) is a liquid's density divided by the density of water at a reference temperature. With water at 4 °C as the reference, as in the tables above, water's own SG falls from 1.0000 at 4 °C to 0.9584 at 100 °C. The petroleum industry and many US engineering references use water at 60 °F (999.02 kg/m³) as the reference instead. To convert an SG on the 60 °F basis to the 4 °C basis, multiply by 0.9990.

A pump curve gives head in feet of the liquid pumped and a gauge reads psi, and SG converts between them. 100 ft of head in water at 80 °C reads 42.1 psi, against 43.3 psi at 20 °C. The psi to feet of head converter does this for any SG.

Using Water Density in Calculations

Mass is volume times density. 1,000 litres (1 m³) of water at 20 °C has a mass of 998.2 kg, and 1,000 US gallons at 60 °F weigh 8,337 lb. To find the volume first, use the tank calculator or the pipe volume calculator.

Density also sets the pressure under a column of water, P = ρgh, and the power a pump needs to lift it. 10 m of water at 20 °C exerts 998.207 × 9.80665 × 10 = 97,891 Pa (97.9 kPa); the same 10 m at 80 °C exerts 95.3 kPa. The Reynolds number calculator uses these same densities, with the viscosity at each temperature, and the mass flow rate calculator converts a volume flow to kg/s.

Where These Figures Come From

The densities are for pure liquid water at 101.325 kPa (1 atm) from the IAPWS-95 formulation, the international standard behind the NIST water property tables, evaluated every 5 °C from 0 to 100 °C. The 100 °C row is saturated liquid, as water boils at 99.97 °C at 1 atm. Between rows, the lookup and the °F table use a cubic through the four nearest rows, which stays within 0.001 kg/m³ of the full formulation.

Dissolved salts raise the density, so seawater is about 1,025 kg/m³, and pressure raises it slightly. For anything other than fresh water, use the liquid's own figure from its datasheet.