Altitude Boiling Point Calculator | Water Temperature at Elevation

What the calculator does

The altitude boiling point calculator finds the temperature at which water boils at a given elevation above sea level. Water boils cooler as altitude increases, because there is less air pressing down from above. At sea level water boils at 100 °C (212 °F). On Mount Everest's summit, 8,848 m up, it boils at about 70 °C (158 °F).

Enter an elevation and the tool returns the boiling point in Celsius and Fahrenheit, plus the local air pressure. This matters for cooking, food safety, brewing, and lab work, all of which depend on how hot boiling water actually gets.

Why water boils cooler at altitude

Water boils when its vapor pressure — the push of steam trying to escape the liquid — equals the pressure of the air pressing down on it. At sea level, air pressure is high, so water has to get all the way to 100 °C before its vapor pressure can match it. Higher up, the air is thinner and pushes down less hard, so water reaches that balance point at a lower temperature.

Boiling point of water by altitude

How to calculate boiling point at altitude

The calculation has two steps: turn altitude into air pressure, then turn air pressure into a boiling point.

Step 1: altitude to air pressure

Air pressure drops in a predictable way as altitude increases. The tool uses the International Standard Atmosphere (ISA) barometric formula, which holds through the troposphere, from sea level up to about 11 km:

$P_{\text{inHg}} = 29.921 \times \left(1 - 6.8753\times10^{-6} \times h_{\text{ft}}\right)^{5.2559}$

Here $h_{\text{ft}}$ is altitude in feet, and $P_{\text{inHg}}$ is the local pressure in inches of mercury (a unit meteorologists use for barometric pressure).

Step 2: air pressure to boiling point

Water boils once its vapor pressure equals the surrounding air pressure, so the boiling point at a given altitude is just the saturation temperature of water at that pressure. A simple straight-line fit between pressure and temperature looks tempting, but the real curve bends: a line anchored at sea level drifts several degrees too low by the time it reaches high altitude.

To avoid that error, the calculator uses the IAPWS-IF97 formula, the international standard equation for water and steam properties published by the International Association for the Properties of Water and Steam. It gives the exact saturation temperature for any pressure between water's triple point (where ice, liquid, and vapor can all exist together) and its critical point (where the distinction between liquid and gas disappears):

$T_s(\text{K}) = \text{IAPWS-IF97 Region 4 saturation-temperature equation, } T_s(P)$ $T(°C) = T_s(\text{K}) - 273.15, \qquad T(°F) = T(°C) \times \tfrac{9}{5} + 32$

The full equation combines ten fitted coefficients with a pressure term raised to the power 0.25, then solves a quadratic. It is not something to work out by hand, but it reproduces laboratory-measured steam tables almost exactly, which is why it is the equation power-plant and steam-table engineers rely on.

Worked example

Denver, Colorado, sits at about 1,609 m (5,280 ft), earning it the nickname "the Mile High City."

1. Convert to feet: 1,609 m × 3.28084 = 5,280 ft.
2. Plug into the pressure formula: $P = 29.921 \times (1 - 6.8753\times10^{-6} \times 5{,}280)^{5.2559} \approx 24.64$ inHg, which converts to about 83.4 kPa.
3. Look up the saturation temperature for 83.4 kPa using the IAPWS-IF97 equation: about 94.6 °C (202.3 °F).

So water in Denver boils at roughly 94.6 °C instead of 100 °C — about 5.4 °C cooler than at sea level.

Accuracy and limits

• Below about 11 km: the pressure-to-temperature step is essentially exact, since it is the same equation used to build official steam tables. The main source of error is the altitude-to-pressure step, which assumes the standard atmosphere; real weather can shift results by up to roughly 1 °C.
• Above 11 km: altitude leaves the troposphere the barometric formula was built for, so results become an extrapolation. The calculator flags this case.
• Dissolved solids: salt or sugar in the water raise its boiling point slightly. Even heavy salting only adds about 1 °C.
• Below sea level: places like the Dead Sea shore (about 430 m below sea level) have higher air pressure than sea level, so water there boils slightly above 100 °C — about 101.4 °C (214.5 °F).

Why the boiling point matters

• Cooking: at 2,000 m, water tops out around 93 °C. It still looks like a rolling boil, but it is cooler, so pasta, rice, and eggs need longer to cook. A pressure cooker traps steam and raises the internal pressure, pushing the boiling point up to around 121 °C, which is why high-altitude cooks use them.
• Food and water safety: boiling still kills most waterborne pathogens, but the CDC recommends boiling for a full 3 minutes above about 2,000 m instead of 1 minute, since the lower temperature needs more time to work.
• Labs and industry: autoclaves, distillation columns, and reflux setups calibrated at sea level do not behave the same way at elevation and may need adjustment.

Frequently asked questions

Why does water boil cooler at altitude?

Boiling starts when water's vapor pressure matches the surrounding air pressure. There is less air overhead at altitude, so less pressure to match, so water reaches that point at a lower temperature.

How much does the boiling point drop per 1,000 feet?

Roughly 1 °C (about 1.8 °F) per 1,000 ft near sea level. The drop gets slightly steeper at greater heights because air pressure itself falls faster there.

What temperature does water boil at on Mount Everest?

About 70 °C (158 °F) at the 8,848 m summit, compared with 100 °C at sea level. That is one reason melting snow for water takes so long on the mountain.

Does water boil hotter below sea level?

Yes. Below sea level, air pressure is higher than the sea-level average, so water needs a slightly higher temperature before its vapor pressure can match it. At the Dead Sea shore, water boils at about 101.4 °C.

Does this affect cooking times?

Yes. Since the water is cooler, food takes longer to cook by boiling. A common adjustment is adding roughly 15–25% to boiling-water cook times above about 5,000 ft (1,500 m), or switching to a pressure cooker.

How accurate is this calculator?

Within about 1 °C up to 11 km under typical conditions. Unusual weather changes local air pressure and can shift the result slightly; for critical work, measure the actual barometric pressure instead of relying on altitude alone.

References

1. International Association for the Properties of Water and Steam (IAPWS). Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam (IF97), Region 4 saturation equation.
2. NOAA National Weather Service — Standard Atmosphere / pressure–altitude.
3. U.S. Centers for Disease Control and Prevention — Water disinfection while traveling: boiling.
4. Lide, D. R. (ed.). CRC Handbook of Chemistry and Physics — vapor pressure of water tables.
5. U.S. Department of Agriculture, Food Safety and Inspection Service — High-altitude cooking and food safety.