Up high, water boils before it gets to 100 °C (212 °F). Enter your altitude, or a barometer reading, to see the temperature your pot of water really reaches, and how it is worked out.
Water boils at
93.3 °C
200.0 °F
6.7 °C lower than at sea level
Air pressure 795 hPa, 78% of sea level
Point at the chart to read off any altitude.
| Altitude | Air pressure | Boils at | Boils at |
|---|---|---|---|
| 0 m | 101.3 kPa | 100.0 °C | 212.0 °F |
| 500 m | 95.5 kPa | 98.3 °C | 209.0 °F |
| 1,000 m | 89.9 kPa | 96.6 °C | 206.0 °F |
| 1,500 m | 84.6 kPa | 95.0 °C | 203.0 °F |
| 2,000 m | 79.5 kPa | 93.3 °C | 200.0 °F |
| 2,500 m | 74.7 kPa | 91.6 °C | 197.0 °F |
| 3,000 m | 70.1 kPa | 90.0 °C | 194.0 °F |
| 3,500 m | 65.8 kPa | 88.3 °C | 190.9 °F |
| 4,000 m | 61.7 kPa | 86.6 °C | 187.9 °F |
| 4,500 m | 57.8 kPa | 84.9 °C | 184.9 °F |
| 5,000 m | 54.0 kPa | 83.3 °C | 181.9 °F |
Water boils when its vapour pressure matches the pressure of the air above it. Climb higher and there is less air above you, so the water boils sooner, at a lower temperature. The USDA puts it at just under 1 °F lower for every 500 feet: about 208 °F at 2,000 feet and 198 °F at 7,500 feet. Anything cooked in boiling water therefore cooks cooler and slower; see cooking times at altitude.
First, the U.S. Standard Atmosphere 1976 gives the air pressure at your height on an average day. Then the Antoine equation, with the constants the NIST Chemistry WebBook lists for water (Bridgeman and Aldrich, valid from about 71 °C to 100 °C), finds the temperature at which water's vapour pressure equals that pressure. We check it against IAPWS-IF97, the international standard for water and steam; the two agree within 0.05 °C at everyday altitudes, and our results are within 1 °F of the USDA and Colorado State University tables.
Real air pressure rises and falls with the weather, so on a stormy day water boils a little cooler. A weather report's pressure is adjusted to sea level: choose Weather report and we scale it to your altitude. A barometer at your location reads the actual pressure, so use My barometer.
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Check a site with WebTraceCheckNo. Turning up the heat only boils the water away faster; it cannot get hotter than its boiling point. Only a pressure cooker raises it.
Weather changes the pressure, and thermometers vary. Colorado State and New Mexico State extension services suggest testing the temperature of your own boiling water before candy making.
About 70 °C in the standard atmosphere. Real pressure on the summit is a little higher: in 1983, West and colleagues measured 253 mmHg there, which gives about 72 °C.