Boiling point at altitude calculator

Water boils when its vapour pressure matches the air above it. Less air means a lower boiling point and slower cooking.

Altitude

Water boils at

93.22degrees C

≈ Rounded Boiling point at altitude

Below the sea-level boiling point: 6.78 K
Air pressure: 79.495 kPa
Share of sea-level pressure: 78.46 %
Rough cooking-time multiplier Reaction rates roughly halve for every 10 K drop.: 1.600
Altitude in feet: 6562

Show the working

Altitude = 2000
pressure = 101325 * (1 - 2.25577e-5 * 2000)^5.25588 = 79 495.2
Air pressure = 79 495.2 / 1000 = 79.4952
Water boils at = 1 / (1/373.15 - 8.314462618153324 * ln(79 495.2/101325) / 40660) - 273.15 = 93.217
Below the sea-level boiling point = 100 - 93.217 = 6.783 02
Rough cooking-time multiplier = 2^(6.783 02/10) = 1.600 25
Altitude in feet = 2000 * 3.280839895013123 = 6561.68
Share of sea-level pressure = 79 495.2 / 101325 * 100 = 78.4557

Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.

Scenarios & local history

The formula

barometric formula for the troposphere: p = 101325 (1 - 2.25577e-5 h)^5.25588
Clausius-Clapeyron: 1/T = 1/373.15 - R ln(p/p0) / L, with L = 40 660 J/mol for water

At 2000 m water boils near 93 degrees Celsius, and a hard-boiled egg takes noticeably longer.

The barometric formula assumes the International Standard Atmosphere. Real weather moves pressure by a few percent either way.

Boiling point at altitude calculator