Boiling point falls with altitude

Water boils about 1 °C cooler for every 300 m of altitude.

Why it works

Lower pressure means less energy needed to boil. At 3,000 m water boils near 90 °C — food takes noticeably longer.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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More in Environmental

• Lightning distanceCount the seconds from flash to thunder, divide by 3 for kilometres (by 5 for miles).
• Air cools as you climbTemperature drops about 6.5 °C for every 1,000 m of altitude.
• Pressure halves every ~5.5 kmAtmospheric pressure falls by half roughly every 5,500 m you climb.
• Ten metres of water = one atmosphereEvery 10 m of seawater adds about 1 atmosphere of pressure.

Why does water boil at a lower temperature at altitude?

Water boils about 1 °C cooler for every 300 m of altitude. Lower pressure means less energy needed to boil.

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