Water Density Calculator — Density vs Temperature
Find the density of pure water at any temperature from 0 to 100 °C using the standard Kell (1967) polynomial. The calculator shows specific volume, volume for a given mass, and how much your temperature deviates from the 3.98 °C maximum-density point.
°C
kg
1.7686 kg/m³ below maximum (at ~3.98 °C)
- 1
Temperature (T)
20 - 2
Water density (Kell 1967)
999.843 + 6.794×10⁻² × 20 − 9.095×10⁻³ × 20² + 1.002×10⁻⁴ × 20³ − 1.120×10⁻⁶ × 20⁴ + 6.536×10⁻⁹ × 20⁵ = 998.206Kell (1967) 5th-order polynomial for pure water at atmospheric pressure.
How does this calculator work?
Pure water is densest at ~3.98 °C (≈999.975 kg/m³) due to hydrogen bonding. Above and below that temperature, density decreases. At 20 °C density is 998.2 kg/m³; at 100 °C it is 958.4 kg/m³. Use ρ = 999.842594 + 6.79×10⁻² T − 9.10×10⁻³ T² + … (Kell 1967) for pure water at atmospheric pressure.
Formula
How this is calculated
Pure water reaches its maximum density of approximately 999.975 kg/m³ at about 3.98 °C — slightly above the freezing point. This anomalous behaviour arises from the structure of hydrogen bonding: as water cools from room temperature toward 4 °C, the denser tetrahedral hydrogen-bond network grows stronger and pulls molecules closer. Below 4 °C, the open lattice of ice begins to form, causing the liquid to expand slightly again before it freezes at 0 °C. This is why ice floats and why lakes freeze from the surface down rather than from the bottom — a property critical for aquatic life.
Above 4 °C, water density decreases smoothly with temperature as molecules gain kinetic energy and spread further apart. At 20 °C (standard laboratory temperature) density is 998.204 kg/m³; at 100 °C it drops to 958.3 kg/m³. The Kell (1967) polynomial captures these changes with very high accuracy — error is less than 0.003 kg/m³ between 0 and 40 °C, and less than 0.2 kg/m³ up to 100 °C.
The specific volume (litres per kilogram) is the reciprocal of density scaled by 1 000, useful for converting between mass and volume. This calculator covers pure water at atmospheric pressure (101.325 kPa). Seawater, saline solutions, and water under elevated pressure all have higher densities and require separate equations.
Frequently asked questions
Water molecules form hydrogen bonds that pull them into a denser tetrahedral arrangement as temperature falls from room temperature toward 4 °C. Below 4 °C, the bonds start reorganising into the open hexagonal lattice of ice, which is actually less dense. This results in a density maximum at 3.98 °C — unique among common substances and vital for freshwater ecosystems.
Specific volume is the volume occupied by one unit of mass — the reciprocal of density. For water at 20 °C: density = 998.2 kg/m³, so specific volume = 1/998.2 m³/kg ≈ 1.001 8 L/kg. It is particularly useful in engineering calculations where you know the mass of water and need to find the volume, or vice versa.
No. The Kell polynomial is for pure (distilled) water at atmospheric pressure. Dissolved salts significantly increase density — seawater at 35 g/kg salinity and 20 °C has a density of about 1024 kg/m³, roughly 2.6% higher than freshwater at the same temperature. Seawater density requires separate formulas such as the TEOS-10 standard.
Also known as
TG we-Calculate Editorial Team. (2026). Water Density Calculator — Density vs Temperature [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/water-density-calculator
TG we-Calculate Editorial Team. "Water Density Calculator — Density vs Temperature." TG we-Calculate. 2026. https://we-calculate.com/calculator/water-density-calculator.
TG we-Calculate Editorial Team, "Water Density Calculator — Density vs Temperature," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/water-density-calculator
@misc{wecalculate_water_density_calculator, title = {Water Density Calculator — Density vs Temperature}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/water-density-calculator}}, year = {2026}, note = {TG we-Calculate} }
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