Water vapor pressure and boiling point converter
Find the vapor pressure of water at a temperature, or the temperature at which water boils at a pressure.
At 100 °C water’s vapor pressure is 101.3 kPa (14.7 psi): water boils at that temperature when the pressure is that low.
What it means
How hot is that?
Antoine equation for pure water, 1 to 374 °C (two sets of constants); within about 0.5 % of steam tables.
Every unit
That point in every unit
Learn
Three things worth knowing
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Boiling point follows pressure
1 atm: 100 °C. Half an atmosphere: 82 °C. Two atmospheres: 121 °C.
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Antoine’s equation
French engineer Louis Antoine proposed his three-constant formula in 1888; it is still the standard quick fit.
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Gauge or absolute
A pressure cooker’s 15 psi is above atmosphere: 2 atm absolute. Use absolute pressure here.
Shortcuts
Popular temperature conversions
Background
About vapor pressure
Water always evaporates a little; the pressure of that vapor when it is in balance with the liquid is the saturation vapor pressure. It rises steeply with temperature: 2.3 kPa at 20 °C, 101.3 kPa at 100 °C.
Water boils when its vapor pressure equals the pressure around it, which is why it boils at 100 °C at sea level, about 70 °C on Everest and 121 °C in a pressure cooker.