Article — Boiling Point at Altitude Calculator
Boiling point at altitude calculator
Water boils at 100 °C (212 °F) at sea level, but the boiling point drops about 1 °C per 295 m (1 °F per 540 ft) of altitude gain. Denver at 1,609 m boils water at 94.7 °C. La Paz at 3,640 m boils water at 88.4 °C. The summit of Everest at 8,849 m boils water at just 70.5 °C — barely warm enough for a hot cup of tea.
The physics is straightforward: water boils when its vapour pressure equals the surrounding atmospheric pressure, and atmospheric pressure falls as you climb. Combine the US Standard Atmosphere with the Antoine vapour-pressure equation and you have a robust altitude-to-boiling-point calculator that matches measured values within about 0.2 °C up to 5,000 m.
Water boiling point at altitude
Water boiling point at altitude is the temperature at which water transitions to vapour under reduced atmospheric pressure. At sea level, where pressure is 1 atm (101,325 Pa, 760 mmHg), pure water boils at exactly 100 °C. Climb 1 km and pressure falls to about 887 mbar, and boiling drops to roughly 96.7 °C. The relationship is non-linear because both pressure-versus-altitude and vapour-pressure-versus-temperature are exponential.
The implication for cooking is that food cooks more slowly even with the lid on, because the maximum temperature water can reach is set by the boiling point. At 3,000 m a pot of boiling water sits at 90 °C, meaning eggs, beans, and pasta need 20–60% more time depending on what is being cooked.
Why altitude changes the boiling point
Boiling is a phase change governed by vapour pressure equilibrium. As water heats, its molecules gain kinetic energy and more of them escape into the vapour phase. The pressure those escaped molecules exert is the vapour pressure. When the vapour pressure equals the external atmospheric pressure, bubbles can form throughout the liquid — that is boiling.
At higher altitudes, fewer air molecules sit above any point on Earth, so atmospheric pressure is lower. The vapour pressure needs to match that lower pressure, which it does at a lower temperature. The relationship is captured by the Clausius–Clapeyron equation in differential form, or by the more practical empirical Antoine equation in everyday calculations.
You can boil water at room temperature without any heating. Place a beaker in a vacuum chamber and pump it down to about 23 mmHg (3% of sea-level pressure). Water starts boiling at 25 °C. Freeze-drying technology — used for instant coffee, MREs, and pharmaceuticals — depends on exactly this trick: water evaporates from frozen samples at low pressure without ever passing through the liquid phase.
The boiling point altitude formula
Two equations chain together. The US Standard Atmosphere gives pressure as a function of altitude in the troposphere. The Antoine equation gives the temperature at which water's vapour pressure equals any given external pressure.
P(h) = P₀ × (1 − 0.0065h/288.15)^5.2561 US Standard Atmospherelog₁₀ P = A − B/(C + T) Antoine equationA = 8.07131, B = 1730.63, C = 233.426 water, 1–100 °C, P in mmHgT_bp = B/(A − log₁₀ P) − C solve for boiling pointA quick mental-math shortcut: boiling point drops about 0.34 °C per 100 m gain in the first kilometre, and slightly more per metre as altitude increases. In US units, that is about 1 °F per 540 ft from sea level to mid-elevations. Higher up the rate steepens because pressure falls exponentially.
Boiling point by elevation
Water boiling temperatures at common landmarks and cities, computed from the formulas above.
- Sea level (0 m): 100.0 °C / 212.0 °F. Reference standard.
- Denver (1,609 m / 5,280 ft): 94.7 °C / 202.5 °F. Mile-High City.
- Bogotá (2,640 m): 91.7 °C / 197.1 °F. Colombian capital.
- Mexico City (2,240 m): 92.7 °C / 198.9 °F. North American megacity.
- Lhasa (3,656 m): 88.3 °C / 190.9 °F. Tibetan plateau.
- La Paz (3,640 m): 88.4 °C / 191.1 °F. Highest capital city.
- Mount Whitney (4,418 m): 85.5 °C / 185.9 °F. Highest peak in lower 48 US states.
- Everest base camp (5,364 m): 82.5 °C / 180.5 °F.
- Everest summit (8,849 m): 70.5 °C / 158.9 °F. Tea barely steeps.
High-altitude cooking and baking
Two things change at altitude. Boiling water is cooler, so wet-cooking methods are slower. Atmospheric pressure is lower, which affects baking because rising dough expands more aggressively before the structure sets.
Boiling adjustments: extend cook times by 25% above 1,500 m, by 50% above 2,500 m, and double them above 3,500 m for tough foods like beans, dried legumes, and large potatoes. Pasta still cooks in roughly the same time because it needs less heat penetration, but it absorbs more water along the way and can become mushy if not watched.
Baking adjustments above ~900 m: reduce baking powder/soda by 25%, reduce sugar by 1–2 tablespoons per cup, and add 1–4 tablespoons of liquid per cup. Bake at slightly higher temperature (about 8–14 °C / 15–25 °F warmer) to set the crumb before over-rising collapses it.
Pressure cookers and vacuum chambers
A pressure cooker raises absolute pressure above atmospheric to lift the boiling point. A standard 15-psi gauge cooker holds about 2 atm absolute, where water boils at 121 °C (250 °F). The 21 °C extra cooks beans and tough cuts of meat in a fraction of the open-pot time, and is the basis of pressure canning for low-acid foods — 121 °C is hot enough to destroy Clostridium botulinum spores.
USDA pressure-canning guides specify higher processing pressures above 1,000 ft because the atmospheric component of the gauge reading is reduced at altitude. At 5,000 ft above sea level, use 13 psi gauge instead of 11 psi for the same actual canner temperature. Skipping the correction can leave low-acid foods under-processed and unsafe.
Common altitude cooking mistakes
Above 2,000 m, soft-boiled eggs need a different recipe entirely. Water at 92 °C cannot reach the 71 °C white-set temperature internally in the standard 4–5 minutes because heat transfer is slower. Use a covered pot, add 30–60 seconds, and ice-bath immediately.
The first mistake is assuming higher heat means faster cooking. A pot at full burner with vigorously boiling water at 90 °C still cannot exceed 90 °C — extra flame just evaporates water faster, not cook food faster. The fix is to extend time, not crank heat.
The second mistake is ignoring the air-pressure side of baking. At altitude, gases trapped in dough expand more before the dough sets, so over-leavened cakes rise spectacularly and then collapse. Cut leavening, add liquid, and use a slightly hotter oven to firm structure before the rise outpaces it.
The third mistake is confusing weather pressure with altitude pressure. A storm at sea level can drop pressure 25 mmHg below standard, shifting boiling by about 1 °C. That is not enough to ruin cooking but it does explain why a recipe behaves differently on stormy days. Altitude effects dwarf weather effects above 1,500 m.