How this calculator works
Altitude is converted to pressure using the tropospheric U.S. Standard Atmosphere, then to boiling temperature using constant-enthalpy Clausius-Clapeyron for pure water. The altitude input is geopotential height, closely approximated by ordinary elevation over this range. Weather changes actual pressure; the model is an average atmosphere. Water impurities, dissolved salt and pressure vessels are excluded. The model accepts -500 to 11000 m and uses a 373.15 K, 101325 Pa water reference.
Formula
P = 101325 [1 - 0.0065 h/288.15]^(g M/(Rair 0.0065)); 1/Tboil = 1/373.15 - (R/40650) ln(P/101325).
Worked example
At sea level, estimated pressure is 101.325 kPa and water boils at 100 C. At 1000 m geopotential height, pressure is about 89.875 kPa and the estimate is about 96.6 C.
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Frequently asked questions
Does weather affect this result?
Yes. A measured local absolute pressure gives a better boiling-point estimate than altitude alone.
Why stop at 11 km?
Above the troposphere the standard-atmosphere temperature profile changes and needs another equation.
Does this set cooking times?
It estimates temperature only. Food, equipment and cooking procedures also determine timing.