Air pressure falls as you climb, because there is less air above you pressing down. At sea level the standard pressure is 101.325 kPa; at 1,500 m it is about 84.6 kPa, and on the summit of Everest only about a third of that. Water boils when its vapour pressure matches the air pressure, so the higher you go, the lower the boiling point – roughly 1 °C for every 300 m near sea level.
This matters in the kitchen and in the lab. Pasta, beans and eggs take longer to cook at altitude because the water is cooler, baking recipes need adjusted leavening and liquid, and sterilising by boiling becomes less effective above about 2,000 m – the reason pressure cookers are popular in mountain towns.
Enter an altitude (or, if you have a barometer, the actual air pressure). The calculator uses the International Standard Atmosphere for pressure, then solves for the boiling point of pure water with the method you pick. Weather changes real pressure by a few kPa, which shifts the boiling point by up to about 1 °C.
How to use the Boiling Point at Altitude Calculator
- I know
- Altitude above sea level
- Air pressure (absolute, not sea-level corrected)
- Method
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
First the altitude is turned into pressure with the barometric formula of the standard atmosphere. Then the boiling point is the temperature at which water’s vapour pressure equals that pressure: the Antoine equation is inverted directly, the Clausius–Clapeyron option uses ΔHvap = 40.65 kJ/mol from the normal boiling point, and the empirical option is the widely quoted fit T(°F) = 49.161 · ln P(inHg) + 44.932.
Worked example
At 1,500 m: P = 101.325 × (1 − 2.25577 × 10⁻⁵ × 1500)^5.25588 = 84.56 kPa = 634.2 mmHg. Antoine: log₁₀ 634.2 = 2.8023, so T = 1730.63 / (8.07131 − 2.8023) − 233.426 = 328.45 − 233.43 = 95.0 °C (203.0 °F), five degrees lower than at sea level.
Boiling point of water by altitude
| Altitude | Air pressure (ISA) | Water boils at |
|---|---|---|
| 0 m (0 ft) | 101.3 kPa | 100.0 °C (212.0 °F) |
| 500 m (1,640 ft) | 95.5 kPa | 98.3 °C (209.0 °F) |
| 1,000 m (3,281 ft) | 89.9 kPa | 96.7 °C (206.0 °F) |
| 1,500 m (4,921 ft) | 84.6 kPa | 95.0 °C (203.0 °F) |
| 2,000 m (6,562 ft) | 79.5 kPa | 93.4 °C (200.1 °F) |
| 2,500 m (8,202 ft) | 74.7 kPa | 91.7 °C (197.1 °F) |
| 3,000 m (9,843 ft) | 70.1 kPa | 90.0 °C (194.1 °F) |
| 4,000 m (13,123 ft) | 61.6 kPa | 86.7 °C (188.0 °F) |
| 5,000 m (16,404 ft) | 54.0 kPa | 83.3 °C (182.0 °F) |
| 8,849 m (29,032 ft) | 31.4 kPa | 70.3 °C (158.5 °F) |
Standard-atmosphere pressure; boiling point from the Antoine equation.
Tips
- Use kelvin for every temperature in thermodynamic formulas – the unit menus convert for you.
- Watch the units: ΔH is usually in kJ/mol and ΔS in J/(mol·K).
- Tabulated values are for standard conditions (1 bar, usually 25 °C).
- Everything is calculated in your browser.
Common mistakes to avoid
- Mixing kJ and J between ΔH and ΔS.
- Assuming ΔH and ΔS do not change with temperature over large ranges.
- Using Celsius in ln(T₂/T₁).
Inputs explained
| Field | What to enter |
|---|---|
| I know | Choose one: My altitude, The air pressure |
| Altitude above sea level | Units: m, ft, km, mi |
| Air pressure (absolute, not sea-level corrected) | Units: kPa, atm, bar, hPa (mbar), mmHg (Torr), psi … |
| Method | Choose one: Antoine equation (most accurate), Clausius–Clapeyron (ΔHvap = 40.65 kJ/mol), Empirical formula 49.161·ln P + 44.932 (°F, inHg) |
What each result means
- Air pressure = [P]÷101.325
- Lower than at sea level by = 99.97 – [Boiling point of water]
- Pressure as a share of sea-level pressure = ([P]÷101.325)×100
Formula
P = 101.325 kPa × (1 − 2.25577 × 10⁻⁵ × h)^5.25588 (h in m) · Antoine: T = B / (A − log₁₀ P) − C with A = 8.07131, B = 1730.63, C = 233.426 (P in mmHg, T in °C)Worked example
Inputs — I know: My altitude; Altitude above sea level: 1,500 m; Method: Antoine equation (most accurate).
Results — Air pressure = 84.556 kPa; Boiling point of water = 95.025 °C; Lower than at sea level by = 4.945 °C (= K); Pressure as a share of sea-level pressure = 83.5 %; Cooking note = Slightly longer cooking times (a few minutes for pasta and eggs).
Key terms
- Barometric formula
- An equation giving air pressure as a function of height for a model atmosphere.
- International Standard Atmosphere (ISA)
- A reference atmosphere with 101.325 kPa and 15 °C at sea level and a temperature lapse rate of 6.5 °C per km.
- Antoine equation
- An empirical vapour-pressure equation log₁₀ P = A − B/(C + T) with constants fitted for each substance.
- Absolute pressure
- The true pressure of the air, as opposed to the sea-level-corrected value quoted in weather reports.
Frequently asked questions
At what temperature does water boil in Denver?
At 1,609 m (5,280 ft) the standard pressure is about 83.4 kPa and water boils at about 94.6 °C (202 °F).
How much does the boiling point drop per 1,000 feet?
About 1 °F per 500 ft, or roughly 1 °C per 300 m, near sea level. The drop slows slightly at very high altitude.
What is the boiling point on Mount Everest?
At 8,849 m the standard-atmosphere pressure is about 31.4 kPa, giving a boiling point near 70 °C (158 °F).
Does weather change the boiling point?
Yes. A deep low-pressure system can lower sea-level pressure by 3–5 kPa, which lowers the boiling point by about 1 °C.
Why does food take longer to cook at altitude?
Cooking speed depends on temperature, not on bubbling. Water boiling at 93 °C cooks more slowly than water at 100 °C, even though both are "boiling".
Is the boiling point lower below sea level?
No – higher. At the Dead Sea shore (about −430 m) pressure is about 106.6 kPa and water boils near 101.4 °C.
Which method should I choose?
The Antoine equation fits measured water data closely between 1 and 100 °C; the other two methods agree with it within about 0.3 °C up to 3,000 m.