Estimate the boiling point of pure water from altitude or local air pressure, then compare it with sea level in F, C, or both.
Advanced options
How to use our Boiling Point at Altitude Calculator
- Pick "What do you know?" and choose either altitude or air pressure.
- Enter either "Altitude (ft)" or "Air pressure (kPa)". If needed, open "Advanced options" and change "Altitude unit" or "Pressure unit" to match your number.
- Choose "Show result in" for F, C, or both, then calculate.
- Read "Boiling point of water" first, then check "Change from sea level" and "Estimated air pressure (kPa)" to see why the temperature changed.
- Sanity-check the answer: at sea level water should be about 212 F or 100 C, and higher altitude usually gives a lower boiling point.
Definitions
Altitude (ft): Height above sea level. Higher altitude usually means lower air pressure.
Air pressure (kPa): The push of the air around the water. This is the direct factor that sets the boiling point.
Estimated air pressure (kPa): The pressure calculated from altitude using a standard-atmosphere model, not a live local weather measurement.
Boiling point of water: The temperature where pure water's vapor pressure matches the surrounding air pressure.
Change from sea level: How much the calculated boiling point differs from the usual sea-level value of 100 C or 212 F.
Pressure unit: The unit used for your pressure entry, such as kPa, atm, mmHg, or inHg.
Antoine equation: A standard formula used to estimate the temperature of pure water from pressure over a limited range.
Common mistakes and quick fixes
Mistake: Entering a negative value in "Altitude (ft)".
Fix: Use 0 or higher for "Altitude (ft)". This calculator does not estimate below-sea-level cases.
Mistake: Typing pressure in mmHg or atm but leaving "Pressure unit" on kPa.
Fix: Change "Pressure unit" so it matches your "Air pressure (kPa)" entry before you calculate.
Mistake: Comparing recipes in F, but reading only "Boiling point of water (C)".
Fix: Set "Show result in" to "F only" or "F and C" so the output matches the temperature scale you use.
Mistake: Expecting "Change from sea level" to always be positive.
Fix: A negative "Change from sea level" means water boils at a lower temperature than at sea level, which is normal at higher altitude.
Mistake: Reading "Estimated air pressure (kPa)" as a live weather reading.
Fix: In altitude mode, "Estimated air pressure (kPa)" is a standard-atmosphere estimate. If you know your actual local pressure, use "Air pressure (kPa)" mode instead.
Mistake: Using "What this means for cooking" like an exact recipe-time rule.
Fix: Treat "What this means for cooking" as a practical hint only. It explains direction, not an exact number of extra minutes.
Limitations & Key Assumptions / Boundary Conditions
- This calculator is for pure water only. Salt, sugar, and other dissolved substances can change the real boiling point.
- Altitude mode estimates pressure from the standard atmosphere, so local weather and day-to-day pressure changes are not included.
- The water relation used here is best within about 1 C to 100 C for the chosen Antoine constants. Outside that range, the result is less reliable.
- Very high altitudes can fall outside the most appropriate range for the simple standard-atmosphere step used here.
- The cooking note is directional guidance only. It does not predict exact recipe times, doneness, or appliance behavior.
- If local pressure is above standard atmospheric pressure, the calculator can return a boiling point above 100 C, which is physically valid.
Methodology
How the calculator works
If you enter altitude, the calculator first estimates air pressure with a standard-atmosphere equation. If you enter pressure directly, that value is used instead.
P = P0 x (1 - Lh/T0)^(gM/(RL))
After pressure is known, the calculator converts it to mmHg and solves an inverted Antoine equation for pure water to get the boiling temperature in C. Water boils when its vapor pressure matches the surrounding air pressure [2].
T_C = B / (A - log10(P_mmHg)) - C
The calculator then converts the result to F if needed.
T_F = T_C x 9/5 + 32
It also compares the result with the standard sea-level boiling point of water.
change_C = T_C - 100
change_F = T_F - 212
Mini example
Suppose you enter 5,280 ft. The standard-atmosphere step gives an estimated pressure near 83.1 kPa. Converting that pressure and applying the water equation gives a boiling point near 94.9 C, which is about 202.8 F. That is about 5.1 C lower than sea level.
Assumptions used
The altitude-to-pressure step uses standard-atmosphere constants for sea-level pressure 101325 Pa, sea-level temperature 288.15 K, lapse rate 0.0065 K/m, gravity 9.80665 m/s^2, molar mass of air 0.0289644 kg/mol, and gas constant 8.3144598 J/(mol*K). Pressure conversions use 1 atm = 101.325 kPa = 760 mmHg and 1 inHg = 3.386389 kPa.
When real results can differ
Real boiling temperature can differ if your local weather pressure is unusual, if the water is not pure, or if you are far outside the normal range where the chosen Antoine constants fit well. That is why direct pressure mode is usually the better estimate when you already know the local air pressure.