What is saturation vapor pressure?

It is the partial pressure exerted by water vapor when the air is fully saturated at a given temperature. Above this pressure, water vapor condenses.

Which equation is more accurate — Magnus or Buck?

The Buck equation (1981) is slightly more accurate over liquid water for temperatures between -40 °C and 60 °C. The Magnus (Tetens) formula is simpler and widely used in meteorology with error < 0.1 % in the range 0–50 °C.

What units does this calculator output?

Results are shown in hPa (millibars), kPa, mmHg (torr), and inHg — the four units most commonly used in meteorology and engineering.

Does temperature need to be in Celsius?

No. You can enter Celsius or Fahrenheit. The tool converts Fahrenheit to Celsius internally before applying the formulas.

Are these formulas valid for ice?

The formulas used here apply to liquid water. For temperatures below 0 °C the values represent super-cooled liquid water (metastable). Different coefficients are needed for ice.

Saturation Vapor Pressure Calculator

Enter a temperature in Celsius or Fahrenheit and get saturation vapor pressure in hPa, kPa, mmHg, and inHg using both the Magnus (Tetens) and Buck equations.

Input Temperature

Temperature

°C

Valid range: -60 °C to 100 °C

Results

Enter a temperature and click Calculate.

Quick-Reference Table (-20 °C to 50 °C)

T (°C)	Magnus hPa	Buck hPa	mmHg	inHg

Summary

This calculator computes saturation vapor pressure (the maximum water vapor pressure at a given temperature) using the widely-adopted August-Roche-Magnus approximation and the more precise Buck equation. Results are presented in hPa (mbar), kPa, mmHg, and inHg, and a quick-reference table spans -20 °C to 50 °C.

How it works

Enter a temperature and choose Celsius or Fahrenheit; Fahrenheit is converted to Celsius internally.
The tool applies the August-Roche-Magnus (Tetens) approximation and the Buck equation to that temperature.
Saturation vapor pressure is shown side by side in hPa (mbar), kPa, mmHg, and inHg.
Compare your value against the quick-reference table spanning -20 °C to 50 °C in 5 °C steps.

Use cases

Meteorology and weather station calibration.
HVAC and building science humidity calculations.
Agricultural irrigation scheduling based on evapotranspiration.
Laboratory and industrial drying process design.
Educational demonstrations of the Clausius-Clapeyron relation.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu