Vapor Pressure of Water Calculator

Your details

Water temperature. Works from -40 to 374 C (critical point). Switch between Celsius and Fahrenheit.
Choose which formula drives the primary result. All five values are shown in the comparison output.
Vapor pressureLiquid water (subcooled)
3.1685

Saturation vapor pressure of water at the entered temperature

Temperature (C)25C
Buck formula3.1685
Magnus formula3.1617
Tetens formula3.1677
Antoine formula3.1579
Simple formula3.1842
Boiling point at ambient25C
UnitkPa
3.1685 kPa
Very low (near 0 C)<1.2Moderate (0-50 C)1.2-12.3High (50-80 C)12.3-47.4At boiling point47.4-101.3Above boiling101.3+

Saturation vapor pressure at 25.0 C is 3.1685 kPa.

  • At 25.0 C, water does not boil at standard sea-level pressure (101.325 kPa) because its vapor pressure of 3.1685 kPa is below atmospheric.
  • The Buck formula is the most accurate in the 0-100 C range: it matches tabulated NIST data to within 0.04% across that span, outperforming Magnus (+1.13% at 100 C) and the simple exponential (-2.3% at 50 C).
  • Vapor pressure doubles roughly every 10 C for liquid water near room temperature, which is why summer humidity feels so much heavier than winter humidity.

Next stepUse the comparison rows to see how much each formula differs at your temperature. For engineering calculations in the 0-100 C range, the Buck formula is the recommended default.

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