Boiling Point Calculator

The Boiling Point Calculator works out the temperature at which water boils — either from an altitude or directly from an atmospheric pressure — and reports it in °C, °F, and K.

Why water's boiling point changes

Water boils when its vapor pressure equals the surrounding atmospheric pressure. At sea level, standard atmospheric pressure (101.325 kPa) makes that happen at 100 °C. Go up in altitude and the air thins — atmospheric pressure drops — so water boils at a lower temperature. On Denver's Front Range (~1,600 m / 5,280 ft), water boils around 94.7 °C instead of 100 °C.

How it calculates

1. Altitude → pressure. In altitude mode, the calculator first converts your altitude to atmospheric pressure using the US Standard Atmosphere barometric formula:

   P(h) = 101.325 × (1 − 2.25577×10⁻⁵ × h)^5.25588

   where h is altitude in meters. This is accurate through the troposphere (roughly sea level to 11 km / 36,000 ft), which covers virtually every inhabited or hiked elevation on Earth.

2. Pressure → boiling point. Either from that computed pressure, or from a pressure you enter directly, the calculator solves the Antoine equation for water:

   log₁₀(P_mmHg) = A − B / (C + T)

   with the standard NIST coefficients (A = 8.07131, B = 1730.63, C = 233.426), rearranged to solve for T. This form is accurate for 1–100 °C (roughly 4.6–760 mmHg of pressure).

How to use it

1. Choose Calculate from: Altitude or Atmospheric pressure.
2. Enter your value — altitude in meters or feet, or pressure in kPa, atm, psi, mmHg, or bar.
3. Pick a decimal precision if you want more or fewer digits.

The result shows the boiling point in all three temperature scales, a full pressure breakdown across units, and how far below (or above) the sea-level standard of 100 °C you are — the number that actually matters for adjusting a recipe.

High-altitude cooking

Because boiling water is cooler at altitude, anything that relies on a rolling boil to cook — pasta, eggs, rice, vegetables — takes longer than a sea-level recipe says. A widely used rule of thumb is to add roughly 5% more cook time for every 500 m (1,600 ft) of elevation. Above about 1,000 m (3,280 ft), the USDA recommends pressure canning rather than a boiling-water bath, since standard water-bath canning can no longer reach a temperature high enough to be food-safe.

Why isn't the sea-level result exactly 100.00 °C?

The Antoine equation is a curve fit to real measured vapor-pressure data, not an exact physical law — at standard pressure it lands at 99.99–100.00 °C depending on rounding, which is well within the accuracy real cooking and lab work need.

What altitude range is this accurate for?

Roughly -500 m to 11,000 m (about -1,640 ft to 36,089 ft) — from below the Dead Sea to above Everest's summit and up to the edge of the troposphere. Pressure mode accepts any positive pressure, but results far outside 4.6–760 mmHg (about 0.6–101 kPa) are extrapolated beyond the Antoine equation's fitted range and less precise.

Privacy

All calculations run entirely in your browser. Your figures are never uploaded or stored.