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 grows by roughly a quarter for every 1,000 m, which is what the calculator’s rule of a doubling per 10°C gives
• Baking: liquids evaporate faster at altitude; reduce leavening agents by 25%
• Drinking water: boiling makes it safe at any height people live at. Above 2,000 m (6,500 ft) the CDC says hold a rolling boil for 3 minutes instead of 1.
• Canning is a different matter. Boiling never sterilises low-acid food, even at sea level, so that needs a pressure canner wherever you are, and water-bath times for acidic food get longer as you climb.

Pressure Cooker at Altitude:

A pressure cooker raises the boiling point above 100°C whatever your altitude. At sea level, 15 psi over the outside air takes water to about 121°C. The gauge counts pressure above the air around it, so up high the same setting runs a few degrees cooler, which is why canning guides raise the pressure as you go higher. It is still standard kit in high-altitude kitchens, and it is how autoclaves work.