Chemistry
Vapor Pressure of Water Calculator
Find the saturation vapour pressure of water using your choice of validated correlation.
Your inputs
Change any value to update the result instantly.
Saturation vapour pressure
31.6853 hPa
In kPa
3.1685 kPa
In mmHg
23.766 mmHg
Actual vapour pressure at your humidity
31.6853 hPa
Correlation used
Buck (1996)
Valid range
−40 °C to 50 °C
Each correlation carries its own coefficients and its own valid temperature window; they are never mixed. Outside the stated range the figure is an extrapolation.
What this calculator does
Gives the saturation vapour pressure of water from a selected, validated correlation, plus the actual vapour pressure at your humidity.
What your result means
The pressure water vapour exerts when air is saturated at that temperature.
Formula and working
Buck: P = 6.1121 × exp((18.678 − T/234.5) × T / (257.14 + T))
- 1
Collect the inputs
Water or air temperature = 25 °C; Correlation = 1; Relative humidity = 100 %
- 2
Apply the formula
Buck: P = 6.1121 × exp((18.678 − T/234.5) × T / (257.14 + T))
- 3
Result
Saturation vapour pressure = 31.6853 hPa
Frequently asked questions
Symbols and assumptions
- P_sat
- Saturation vapour pressure
- T
- Temperature in °C
- RH
- Relative humidity
- • Each correlation keeps its own coefficients and its own valid temperature range.
- • Pure water over a flat surface.
Sources and review
Reviewed 2026-09-22 · Next review 2027-09-22
- • Coefficients are never mixed between correlations or ranges; outside the range the value is an extrapolation.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
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