Air Pressure at Altitude Calculator
Air pressure at an altitude from the barometric formula — with the standard temperature there, the share of sea-level pressure, the oxygen available compared with sea level, and the altitude that matches a pressure you have measured.
Pressure falls with height because there is less air above.
How the air pressure at altitude calculator works
Pressure falls with height because there is less air above. In the standard atmosphere the temperature drops 6.5 °C per kilometre and pressure follows a power law in that temperature — about 12% less per kilometre near the ground. The oxygen fraction of air stays at 21%, so the oxygen available falls with the pressure: at 3,500 m there is two thirds of sea level's, at Everest's summit a third.
Formula: p = p₀ (1 − 0.0065 h / T₀)^5.2559 (T₀ in kelvin); h = (T₀ / 0.0065)(1 − (p / p₀)^0.1903)
Worked examples
| Inputs | Pressure at altitude (hPa) | Note |
|---|---|---|
| 2,000 m | 794.95 | 795 hPa, 78% |
| Everest | 314.39 | a third of sea level |
| A measured pressure | 794.95 | about 990 m |
FAQFrequently asked questions
How much does pressure fall with altitude?
About 12% per kilometre near sea level, slowing with height: 1,013 hPa at sea level, 900 at 1,000 m, 795 at 2,000 m, 540 at 5,000 m, 337 on Everest.
Is there less oxygen at altitude?
The air is still 21% oxygen, but there is less air. What matters to the body is oxygen partial pressure, which falls in proportion to the total — at 3,500 m it is two thirds of sea level.
What is the standard atmosphere?
An agreed model — 15 °C and 1,013.25 hPa at sea level, cooling 6.5 °C per kilometre — used for altimeters and aircraft performance. Real days differ; enter the day's sea-level pressure and temperature for a better answer.
Why stop at 11,000 m?
Because above the tropopause the temperature stops falling and the formula changes. Everything from valleys to airliner cruise is inside the range.
How does an altimeter use this?
It measures pressure and runs the inverse formula, which is the measured-pressure row here. That is why altimeters must be set to the local sea-level pressure.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Measurement Institute — Australia's measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.