What This Calculator Does
This calculator finds the density of pure liquid water at a given temperature at standard atmospheric pressure. Water’s density is not constant — it peaks near 4°C and decreases as temperature rises further or drops toward freezing.
The Formula
This uses the Kell equation (1975), a widely accepted polynomial fit to measured water density data: ρ(t) = (a1 + a2t + a3t² + a4t³ + a5t⁴ + a6t⁵) ÷ (1 + b1t), where t is temperature in °C and a1–a6, b1 are fitted constants. It is accurate to within a few parts per million across its valid range of 0°C to 100°C at standard atmospheric pressure.
- Water reaches its maximum density of about 999.97 kg/m³ near 4°C, not at 0°C.
- This formula is for pure water; dissolved salts or minerals (as in seawater) increase density and require a different formula.
This uses the standard Kell equation for general scientific, engineering, and educational reference purposes.
Last reviewed August 2026