How this calculator works
Saturation vapour pressure is the equilibrium pressure of water vapour over the chosen condensed surface. The liquid-water option accepts -20 to 100 C; below zero it represents supercooled liquid. The ice option accepts -50 to 0 C. Antoine is reported only from 0 to 99.85 C, Magnus, Tetens and Buck water formulas only through 50 C, and the IAPWS saturation reference only at or above the triple-point temperature. The constant-enthalpy estimate is included for comparison and is less accurate away from its boiling reference. Enhancement factors for moist air are omitted.
Formula
Antoine: log10(Pbar) = 4.6543 - 1435.264/(TK - 64.848). Magnus: PPa = 610.94 exp(17.625 t/(243.04 + t)). Buck: PPa = 611.21 exp[(18.678 - t/234.5)t/(257.14 + t)], t in Celsius.
Worked example
At 0 C, Magnus gives 610.94 Pa, Tetens 610.78 Pa and Buck 611.21 Pa. At 20 C, Buck gives about 2338.34 Pa, equivalent to 2.33834 kPa.
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Frequently asked questions
Is this the actual vapour pressure in a room?
No. Actual water vapour pressure is approximately saturation pressure times relative humidity as a fraction.
Why do some outputs disappear?
Each correlation is shown only within the temperature range supported on this page.
Are ice and liquid pressures identical below zero?
No. Saturation over ice is lower than over supercooled liquid water at the same temperature.