Boiling Point at Altitude Calculator

How Altitude Affects Boiling Point

Water boils when its vapor pressure equals the atmospheric pressure pushing down on it. Climb, and there is less air above you, so the pressure drops and water boils cooler. That changes cooking times, sterilization, and how hot a cup of tea can ever get.

The rule of thumb T_boil(°C) ≈ 100 − (Altitude in metres / 294)

Quick, and good to a few tenths of a degree up to about 2,000 m. Above that it drifts, because pressure falls off exponentially with height while this rule is a straight line.

What this calculator actually does

It works out the pressure first, using the standard barometric formula, then converts that to a boiling point:

P/P₀ = (1 − 2.25577×10⁻⁵ × h)^5.25588

T_boil(°C) = 100 + 28.07 × ln(P/P₀)

The two methods agree closely at low elevation and separate as you climb: at Denver they match, and at Everest Base Camp they differ by most of a degree.

Worked examples

Denver, Colorado (1,609 m): pressure 83.4 kPa, 94.5°C (202.2°F). The rule of thumb gives 94.5°C too.

Kathmandu, Nepal (1,400 m): 95.3°C (203.5°F).

Everest Base Camp (5,364 m): pressure 51.4 kPa, 81.0°C (177.8°F). Here the rule of thumb says 81.8°C, and it is the rule that is wrong.

Effect on Cooking:

• Pasta takes longer: water at 94°C vs 100°C is noticeably slower to cook starch
• Eggs: soft-boil time increases ~15–20% per 1,000m elevation
• Baking: liquids evaporate faster at altitude; reduce leavening agents by 25%
• Sterilization: above 3,000 m, boiling water does NOT reliably kill all pathogens. Use a pressure cooker.

Pressure Cooker at Altitude: A pressure cooker raises the boiling point above 100°C whatever your altitude. At 15 psi overpressure water boils at about 121°C, which is enough for proper sterilization anywhere on Earth. That is why a pressure cooker is standard kit in high-altitude kitchens, and why autoclaves work the way they do.