Boiling point calculator
The boiling point of water at a given altitude above sea level.
Fill in the fields and the result will appear here automatically.
Estimate pure-water boiling temperature from height −430 to 9000 m. Pressure comes from the first standard-atmosphere layer, followed by a constant-latent-heat Clausius–Clapeyron approximation. The form does not measure actual local pressure.
How it works
Formula and logic
p(h)=101325·(1−0.0065 h/288.15)^(gM/(RL)), g=9.80665, M=0.0289644, R=8.314462618, L=0.0065. Then 1/Tb=1/373.15−R·ln(p/101325)/40660; Tb is kelvin, output Celsius. h=0 is the 100 °C reference point.
Example
At 1500 m: p≈84.556 kPa and Tb≈94.919 °C,5.081 °C below 100 °C. At −430 m the model gives≈101.450 °C; this illustrates the product’s lower bound, not a lake’s current level.
Fields and units
- Altitude above sea level — m
How to use
- — Enter height in metres;0 m returns the adopted reference point.
- — A negative “below 100” difference means boiling above 100 °C.
- — Measurement work requires actual pressure and verified water properties; cooking time is not calculated.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- NASA/NOAA 1976: standard layer and geopotential height; constants differ OpenStax: constant-latent-heat Clausius–Clapeyron
- Limitation
- Pure water, the stated reference point and constant 40660 J/mol: an approximation, not a steam-property table. Salinity, solutes, weather and pressure-cooker pressure are not entered. Height bounds are product limits within the adopted model, not a guaranteed accuracy range. The adopted rounded R=8.314462618 means this does not literally reproduce every constant in the 1976 tables.
FAQ
Why does water boil cooler in the mountains?
Boiling starts when the saturated vapour pressure matches the surrounding pressure. High up the air is thin, so the match happens sooner — at a lower temperature. The same thing happens in a vacuum chamber, only more sharply.
Why does food take longer if the water still boils?
Cooking speed is set by the water temperature, not by the fact of boiling. At three kilometres the boiling water is about 90 °C and proteins denature more slowly. A pressure cooker fixes it: raising the pressure raises the boiling point with it.
How accurate is this in real weather?
Pure water, the stated reference point and constant 40660 J/mol: an approximation, not a steam-property table. Salinity, solutes, weather and pressure-cooker pressure are not entered. Height bounds are product limits within the adopted model, not a guaranteed accuracy range.
Why is the lower bound −430 metres?
At 1500 m: p≈84.556 kPa and Tb≈94.919 °C,5.081 °C below 100 °C. At −430 m the model gives≈101.450 °C; this illustrates the product’s lower bound, not a lake’s current level.