How to use the density of water calculator
- Enter the temperature of the water.
- Select Celsius or Fahrenheit as the unit.
- Read the density of water instantly in kg/m³, g/cm³ and lb/ft³.
How the density of water is calculated
This tool uses the Kell (1975) polynomial, which fits experimental measurements of pure liquid water between 0 and 100 C. The formula is:
rho = (a0 + a1*T + a2*T^2 + a3*T^3 + a4*T^4 + a5*T^5) / (1 + b*T)
where T is the temperature in degrees Celsius and the coefficients are:
- a0 = 999.83952
- a1 = 16.945176
- a2 = -7.9870401e-3
- a3 = -46.170461e-6
- a4 = 105.56302e-9
- a5 = -280.54253e-12
- b = 16.879850e-3
For example, at 20 C the numerator evaluates to about 1335.19 and the denominator to about 1.3376, giving a density of water of 998.20 kg/m³. If you enter Fahrenheit, the calculator converts it to Celsius first using C = (F - 32) * 5/9.
Reference table: density of water by temperature
The table below lists common reference values computed with the Kell polynomial. They agree with modern reference tables (CRC Handbook, IAPWS) to within about 0.01 kg/m³; for example, those tables list 998.21 at 20 °C where the Kell polynomial gives 998.20.
| Temperature (°C) | Density (kg/m³) | Density (g/cm³) |
|---|---|---|
| 0 | 999.84 | 0.99984 |
| 4 | 999.97 | 0.99997 |
| 10 | 999.70 | 0.99970 |
| 20 | 998.20 | 0.99820 |
| 25 | 997.04 | 0.99704 |
| 30 | 995.65 | 0.99565 |
| 40 | 992.22 | 0.99222 |
| 50 | 988.04 | 0.98804 |
| 60 | 983.20 | 0.98320 |
| 80 | 971.80 | 0.97180 |
| 100 | 958.36 | 0.95836 |
Why water density matters in practice
Knowing the exact density of water is essential across many fields. In chemistry, preparing solutions by mass requires accurate solvent density; tools like the molarity calculator and dilution calculator rely on this value when converting between volume and moles.
In engineering, buoyancy calculations, pipe flow analysis and cooling system design all depend on how dense the water is at operating temperature. A difference of about 26 kg/m³ between 20 C and 80 C changes pump sizing and heat transfer rates significantly.
In environmental science, thermal stratification in lakes occurs because warmer surface water is less dense than cooler deep water. The maximum density near 4 C drives seasonal turnover that distributes oxygen through the water column.
Common mistakes and edge cases
A frequent error is assuming water always has a density of exactly 1000 kg/m³. That approximation is only close near 4 C. At room temperature (around 20 C), the density of water is about 998.2 kg/m³, a difference of nearly 0.2 percent that matters in precise work.
The Kell polynomial applies only to pure liquid water between 0 and 100 C at standard atmospheric pressure. Dissolved salts and minerals increase the density. Seawater, for instance, is roughly 1025 kg/m³ at the surface due to its salt content.
Ice is less dense than liquid water, about 917 kg/m³, which is why ice floats. This calculator does not cover the solid phase or temperatures outside the 0 to 100 C liquid range. For general mass-volume conversions beyond water, use a dedicated weight and volume converter.
Unit conversions used
The Kell polynomial outputs density in kg/m³. Conversions to other units use exact factors:
- g/cm³: divide kg/m³ by 1000.
- lb/ft³: multiply kg/m³ by 0.062428 (derived from 1 lb = 0.45359237 kg and 1 ft = 0.3048 m).
- g/mL: numerically identical to g/cm³.
When entering Fahrenheit, the conversion to Celsius is exact: C = (F - 32) * 5 / 9. No rounding is applied until the final display step, and the g/cm³ and lb/ft³ values are computed from the unrounded density.
Worked examples
| Example | Input | Result |
|---|---|---|
| Room temperature (20 °C) | Temperature: 20; Temperature unit: C | Density (kg/m³): 998.20; Density (g/cm³): 0.99820; Density (lb/ft³): 62.316; Temperature: 20.0 °C |
| Maximum density (4 °C) | Temperature: 4; Temperature unit: C | Density (kg/m³): 999.97; Density (g/cm³): 0.99997; Density (lb/ft³): 62.426; Temperature: 4.0 °C |
| Boiling point (100 °C) | Temperature: 100; Temperature unit: C | Density (kg/m³): 958.36; Density (g/cm³): 0.95836; Density (lb/ft³): 59.829; Temperature: 100.0 °C |
| Body temperature (98.6 °F) | Temperature: 98.6; Temperature unit: F | Density (kg/m³): 993.33; Density (g/cm³): 0.99333; Density (lb/ft³): 62.011; Temperature: 98.6 °F (37.00 °C) |
| Freezing point (32 °F) | Temperature: 32; Temperature unit: F | Density (kg/m³): 999.84; Density (g/cm³): 0.99984; Density (lb/ft³): 62.418; Temperature: 32.0 °F (0.00 °C) |
FAQ
What is the density of water at room temperature?
At 20 C (68 F), the density of pure water is approximately 998.2 kg/m³ (998.20 from the Kell polynomial), or 0.9982 g/cm³.
At what temperature is water most dense?
Pure water reaches its maximum density at about 3.98 C, where it is approximately 999.97 kg/m³.
Does this calculator account for saltwater?
No. This water density calculator uses the Kell polynomial for pure water only. Dissolved salts increase density; typical seawater is around 1025 kg/m³.
Why is the density of water not exactly 1000 kg/m³?
The value 1000 kg/m³ is a convenient approximation. The actual density varies with temperature, reaching 999.97 kg/m³ near 4 C and dropping to about 958.4 kg/m³ at boiling.
Can I use this above 100 C or below 0 C?
No. The Kell polynomial is valid only for liquid water between 0 and 100 C at standard atmospheric pressure. Outside that range, water is steam or ice.
Is my data sent anywhere?
No. The calculation runs entirely in your browser. Nothing is uploaded to a server.