How this table is built
Each row is evaluated live from the saturation equations rather than transcribed from a reference book. Over liquid water the values come from the IAPWS-95 formulation, the international standard accurate to better than ±0.025% from the triple point to the critical point; over ice they come from Murphy–Koop (2005), the modern reference for the frost point. Below 0 °C the over-water column is the saturation pressure over supercooled liquid water: IAPWS-95 evaluated below its formal 273.16 K (triple-point) lower limit. Treat it as the conventional supercooled-liquid reference, not a claim that IAPWS-95 is validated that far down.
Because the numbers are computed equations applied to temperature — both facts, not creative content — they are free to reuse; the table is released as CC0, with the source equations cited below for scientific traceability. Need a single value at a precise temperature, or a different formula? Use the main calculator, which shows every formula’s deviation from IAPWS-95 at your exact temperature.
Frequently asked questions
Are these vapor pressure values measured or calculated?
They are calculated, not copied. Every value is computed directly from the IAPWS-95 (Wagner–Pruss) saturation equation over liquid water, and the Murphy–Koop 2005 equation over ice — the same verified code that powers the calculators on this site. Computing the values (rather than reproducing a published table) keeps them free to use and lets you regenerate them in any unit.
What temperature range and steps does the table cover?
From −40 °C to 300 °C: 5-degree steps up to 100 °C, then 10-degree steps to 300 °C. The over-water column spans the whole range (below 0 °C it is the saturation pressure over supercooled liquid water), while the over-ice column is shown only at or below 0 °C, where ice exists.
Why do the over-water and over-ice values differ below freezing?
Below 0 °C, water vapor can be in equilibrium with either supercooled liquid water or ice, and the saturation pressure over ice is lower. That difference is exactly why frost forms and why the 'frost point' differs from the 'dew point'. Meteorological relative humidity is conventionally reported over liquid water even below freezing (the WMO convention).
Can I download the data or change units?
Yes. Use the unit selectors to switch the temperature and pressure columns instantly, and the Download CSV button to get the full table as a comma-separated file (temperature in °C and K, plus saturation pressure over water in Pa, kPa and mmHg, and over ice in Pa). The CSV is regenerated from the same equations, so it always matches what you see.
References
Every formula on this page is implemented from, and validated against, the following primary standards and papers.
- IAPWS R6-95(2018) / Wagner & Pruss 2002 — International Association for the Properties of Water and Steam — the reference standard
- Review of the vapour pressures of ice and supercooled water — Murphy & Koop 2005, QJRMS 131:1539
Spotted an error? Let us know — reader corrections are the best review this site gets.