Article — Boiling Point Calculator (Altitude & Pressure)
Boiling point calculator
Water boils at 100 °C only at standard sea-level pressure (1,013.25 hPa). At Denver's 1,609 m altitude it boils at 95 °C. At Mexico City's 2,240 m it drops to 92.6 °C. On the summit of Mt Everest, water boils at 71 °C — too cool to steep tea properly. A pressure cooker reverses the effect, raising the boil to 120 °C at 2 atm.
The relationship is straightforward physics. A liquid boils when its vapor pressure equals the surrounding air pressure. Lower atmospheric pressure means molecules can escape into the gas phase at lower temperatures. The Antoine equation captures the curve numerically for any vapor pressure between 1 mmHg and a few atmospheres.
What is the boiling point?
The boiling point of a liquid is the temperature at which its saturated vapor pressure equals the external pressure pressing down on the liquid surface. Below that temperature, evaporation happens only at the surface; at the boiling point, vapor bubbles form throughout the liquid because the vapor pressure inside the bubble can push back the surrounding liquid.
The standard or normal boiling point is defined at 1 atmosphere (101,325 Pa). For pure water this is 99.974 °C — usually rounded to 100 °C, which was the original 18th-century definition of the Celsius scale's upper anchor before being replaced by the modern triple-point definition.
The 1948 General Conference on Weights and Measures redefined the Celsius scale by anchoring it to the triple point of water (0.01 °C) rather than the boiling point. That shift was tiny — about 0.026 °C — but it meant water no longer boils at exactly 100 °C in modern thermodynamic units. The number is now 99.974 °C at 1 atm. The discrepancy matters only for high-precision metrology.
Boiling point vs altitude
Atmospheric pressure falls with altitude. The US Standard Atmosphere model gives about 12 hPa drop per 100 m near sea level, slowing to 8 hPa per 100 m at 3,000 m. That pressure decrease cuts the boiling point roughly 1 °C for every 300 m of elevation gain.
0 m 100.0 °C / 212 °F500 m 98.4 °C / 209.1 °F1,000 m 96.7 °C / 206.1 °F2,000 m 93.4 °C / 200.1 °F3,000 m 90.0 °C / 194.0 °F5,000 m 83.0 °C / 181.4 °FThe boiling point formula
Two equations are needed. The barometric formula converts altitude to pressure, and the Antoine equation converts pressure to boiling temperature.
Barometric formula (US Standard Atmosphere):
P(h) = P₀ × (1 − 0.0065h / 288.15)^5.2561, where P₀ = 101,325 Pa and h is altitude in meters.
Antoine equation for water (1–100 °C, P in mmHg):
log₁₀(P) = 8.07131 − 1730.63 / (233.426 + T), where T is in °C and the NIST-published constants are A = 8.07131, B = 1730.63, C = 233.426.
Solving for T gives T_boil = B / (A − log₁₀ P) − C. The calculator above chains these two equations so you can input either altitude or pressure and get the boiling temperature.
Water boiling point by location
Real-world altitudes span the meaningful range from below sea level (Dead Sea, −430 m) up to permanent human settlements at over 5,000 m. Here are common reference points.
- Dead Sea (−430 m): 101.4 °C / 214.5 °F. Sea-level baseline plus a small bonus.
- Sea level (0 m): 100.0 °C / 212 °F. The textbook number.
- Denver, Colorado (1,609 m): 95.0 °C / 203 °F. Mile-high city, 5 °C lower.
- Mexico City (2,240 m): 92.6 °C / 198.7 °F. The largest city above 2,000 m.
- La Paz, Bolivia (3,650 m): 88.0 °C / 190.4 °F. Highest national capital.
- Lhasa, Tibet (3,650 m): 88.0 °C / 190.4 °F. Permanent residents pressure-cook nearly everything.
- Everest base camp (5,364 m): 82.1 °C / 179.8 °F. Tea-water hot enough to drink immediately.
- Everest summit (8,849 m): 71.0 °C / 159.8 °F. Below pasteurization temperature.
Pressure cooker boiling point
A pressure cooker reverses the altitude effect by trapping steam. Modern stovetop cookers operate at gauge pressures of 0.7–1 atm above ambient, giving an absolute pressure of 1.7–2 atm. That raises the boiling point of water from 100 °C to roughly 115–120 °C.
The cooking-time savings are dramatic because chemical reaction rates roughly double for every 10 °C rise — the Arrhenius rule of thumb. A bean stew that takes 2 hours at 100 °C cooks in 25–30 minutes at 120 °C. Dried legumes are the canonical pressure cooker beneficiary because they need both heat and time, and the cooker compresses both.
High-altitude cooking adjustments
Above 1,000 m, recipes designed for sea level need adjustment. The lower boiling temperature slows enzymatic reactions, gelatinization of starches and protein denaturation. Pasta cooks slower and never quite as al dente. Beans can refuse to soften no matter how long you simmer them.
Standard pasteurization protocols require holding milk at 72 °C for 15 seconds or 63 °C for 30 minutes. Boiling water above 3,500 m may not reliably kill all pathogens that thrive at lower temperatures. The CDC recommends a 3-minute rolling boil at altitudes above 2,000 m to inactivate Cryptosporidium and Giardia cysts.
Baking is the harder problem at altitude. Lower pressure makes leavening gases expand more, so cakes rise too fast and collapse. King Arthur Flour publishes adjustment charts: at 1,000 m, increase flour by 1 tablespoon and decrease leavening by 1/8 teaspoon per cup of flour. The exact ratios change every 500 m.
Common boiling point mistakes
Use a pressure cooker above 2,500 m. The added pressure restores the sea-level boiling temperature and recovers cooking speed for beans, grains and stews. A 1.5-liter stovetop cooker handles most family-size batches and costs less than a single high-altitude failed recipe.
The most common error is assuming weather pressure changes are negligible. A passing storm can drop surface pressure by 30 hPa, shifting the boiling point by nearly 1 °C. That is small for cooking but significant for laboratory work. Distillation purification protocols specify "atmospheric pressure" precisely because the boiling point of the target compound depends on it.
A second trap is the Antoine equation's validity range. The water constants A = 8.07131, B = 1730.63, C = 233.426 are calibrated for 1–100 °C. Above 100 °C the constants change to A = 8.14019, B = 1810.94, C = 244.485. The calculator above uses the lower-range constants for altitudes from −500 m up; above sea level you can ignore the issue.