Boiling Point at Altitude Calculator

Water’s famous 100 °C is a sea-level fact, not a property of water. Boiling happens when vapour pressure meets air pressure, and air pressure thins with altitude — so on a mountain the kettle boils cooler, the egg cooks slower, and the pressure cooker becomes serious equipment. This calculator chains the two governing equations honestly: the standard-atmosphere barometric formula turns your elevation into a pressure, and the Antoine equation turns that pressure into water’s boiling temperature at it. Enter metres or feet and read the boiling point your kitchen actually lives at.

The Two Equations Behind the Answer

Step one — pressure from altitude. The international standard atmosphere models air pressure as P = 101.325 × (1 − 2.25577×10⁻⁵ × h)^5.25588 kPa, with h in metres: an exponential-ish decay that halves pressure roughly every 5,500 m. Step two — boiling point from pressure. A liquid boils when its vapour pressure equals the surrounding pressure, and water’s vapour pressure follows the Antoine relation log₁₀P = A − B/(C + T), with constants A = 8.07131, B = 1730.63, C = 233.426 for water (P in mmHg, T in °C). The calculator inverts it — T = B/(A − log₁₀P) − C — at the pressure step one delivered. Both equations are the standard engineering forms, which is why this page’s answers match the tables in the CRC Handbook: the chain is not an analogy or a rule of thumb, and the rule of thumb it reproduces — about 1 °C cooler per 285 m climbed near sea level — can be checked against it at any altitude you like.

Worked Example: A Mile-High Kitchen

The default 1,600 m is Denver’s neighbourhood (the city sits at 1,609 m). Pressure: (1 − 2.25577×10⁻⁵ × 1600) = 0.96391, raised to 5.25588 gives 0.824 — so 83.5 kPa, about 82% of sea-level air. In mmHg, 626.5. Antoine inverted: log₁₀(626.5) = 2.797; T = 1730.63/(8.07131 − 2.797) − 233.426 = 328.1 − 233.4 = 94.7 °C (202.4 °F). Five degrees of boiling point, surrendered to a mile of altitude — and with them, every sea-level cooking time in the book. Reference points along the scale, all from the same two equations: at 1,000 m water boils near 96.7 °C; at 2,000 m, 93.3 °C; at 3,000 m (a high ski town), 90.0 °C; at 5,500 m (Everest base camp is lower, La Rinconada higher), about 81.5 °C; and at the 8,848 m summit itself, near 71 °C — a temperature at which a “boiled” egg remains a permanent rumour, its proteins never properly set.

What Cooler Boiling Does to Cooking

Cooking is chemistry at the water’s temperature, and reaction rates roughly double per 10 °C — so a 5 °C boiling deficit is not a footnote. Boiled and simmered foods at altitude take measurably longer: dried beans and tough grains are the famous casualties, often needing 25–50% more time at 1,600 m, because the water bathing them can never exceed 94.7 °C no matter how violent the boil (a rolling boil is the same temperature as a gentle one — only the bubbles differ). Eggs set by protein denaturation thresholds in the 62–70 °C+ range and merely stretch their timings. Canning and sterilising are the safety-critical case: water-bath canning times are altitude-adjusted by regulation precisely because the bath is cooler, and pressure canning exists to defeat the whole problem. Baking suffers the pressure side directly — gases expand more, leavening over-rises, structure sets late — which is why high-altitude baking adjustments (less leavener, more flour, hotter oven) form their own literature, distinct from the boiling arithmetic on this page but born of the same thinning air.

The Pressure Cooker: Buying the Degrees Back

The pressure cooker is this calculator run in reverse with intent. Seal the pot, let pressure build to a typical 15 psi (about 103 kPa) above ambient, and the boiling point inside is set by the total pressure: at sea level, about 202 kPa absolute, water’s boiling point climbs to roughly 121 °C — the autoclave temperature, which is why the same vessel sterilises. At Denver the gauge adds the same 103 kPa to a thinner base (83.5 + 103 = 186.5 kPa absolute), restoring the interior to about 118 °C — still above sea-level open boiling, which is the entire reason altitude cooks treat the pressure cooker as standard equipment rather than a gadget. Instant-read confirmation for the sceptical: this is also why pressure-canning gauges are altitude-rated — the dial measures pressure above ambient, and ambient is the variable this page computes. Set the calculator to your elevation, add your cooker’s rated pressure, and the Antoine step will tell you the temperature your dinner actually experiences.

The Other Half of Altitude Baking: Gases Expand

Boiling is only the liquid chapter; the pressure itself rewrites the gas chapter of every recipe. A bubble of leavening gas or trapped air occupies volume in inverse proportion to pressure, so at Denver’s 83.5 kPa the same bubble expands to 101.3/83.5 ≈ 1.21 times its sea-level size — 21% more lift arriving earlier in the bake, before the crumb’s structure has set to hold it. Hence the classic high-altitude corrections, each traceable to this page’s pressure figure: slightly less leavening (the air is doing more of the work), a hotter oven (set the structure before the over-expanded bubbles coalesce and fall), and a touch more flour and liquid (strength and moisture against a faster-evaporating, cooler-boiling environment). The boiling point the calculator prints and the cake that slumped are one physics — the standard atmosphere — read at two different stations of the same kitchen.

A Pocket Table of Boiling Points

For the altitudes people actually live and cook at, the calculator’s two equations give (standard atmosphere, water): sea level 100.0 °C; 500 m 98.3 °C; 1,000 m 96.7 °C; 1,500 m 95.0 °C; 2,000 m 93.3 °C; 2,500 m 91.6 °C; 3,000 m 90.0 °C; 4,000 m 86.7 °C. Read the table’s shape, not just its entries: the fall is steepest at the bottom (the first 500 m cost 1.7 degrees) and gentles as the air thins — the pressure curve’s own geometry, which is why the per-500-feet rule of thumb serves valley cooks better than mountaineers, and why the equation, not the rule, is on this page. The table stops at 4,000 m only for compactness; the same two equations, pushed to 8,848 m, return the Everest figure of the worked example — water boiling near 71 °C on the roof of the world, where no open pot has ever cooked a meal properly, and where every expedition kitchen is a pressure vessel by necessity rather than preference.

Related Tools

More from the Chemistry Calculators hub: the Boiling Point Calculator for the solute side of boiling (elevation by dissolved particles), and the live Concentration Calculator for the solution arithmetic that surrounds both.

Frequently Asked Questions

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

About 1 °C per 285 m, which is roughly 1 °F per 500 feet — the classic rule of thumb, accurate near sea level and slightly conservative as you climb (the drop per metre eases at altitude because the pressure curve flattens). The calculator replaces the rule with the two governing equations wherever you live.

Why can’t I just boil harder to compensate?

Because boiling is a temperature ceiling, not a dial: once vapour pressure equals air pressure, additional heat makes steam faster, not water hotter. A furious boil and a lazy simmer are the same temperature to within a fraction of a degree. The only ways up are pressure (a sealed vessel) or solutes (worth tenths of a degree, per the sister calculator).

Does weather change my boiling point?

Yes, modestly: a deep low-pressure system can shave 2–3 kPa off ambient pressure, worth roughly half a degree to a degree of boiling point; a strong high adds a similar amount the other way. Altimeters and this calculator both assume the standard atmosphere — close enough for every kitchen purpose, and the reason expedition cooks recalibrate against the day’s actual pressure.

What happens below sea level?

The mirror image: at the Dead Sea shore (about −430 m), pressure exceeds the sea-level standard and water boils a degree or so above 100 °C. The calculator’s range extends to −500 m for exactly this geography lesson.

Is the Antoine equation exact?

It is an empirical fit, excellent across its fitted range (these constants span roughly 1–100 °C, the whole liquid story below and at ordinary boiling) and the standard engineering source for vapour pressures. At the extremes of the calculator’s range the last decimal is approximate; the first two figures — the ones cooking depends on — are handbook-solid.

At what altitude does water boil at exactly 90 °C?

About 3,000 m — call it 9,800 feet — per the pocket table above. It is a useful landmark: below it, altitude cooking is a matter of longer times; above it, whole categories of technique (sterilising by boiling, reliable dried-bean cooking without pressure) quietly stop working, which is why expeditions above base-camp altitude carry pressure vessels as standard kit.

Why does tea taste different in the mountains?

Extraction chemistry runs on temperature: black tea’s brisk compounds want near-boiling water, and at 90 °C the cup tips toward the soft and under-extracted, while delicate green teas (brewed at 70–85 °C by design) suffer nothing at all. Altitude tea culture adapted empirically centuries before the Antoine constants were fitted — the calculator merely invoices the physics.