Air Pressure at Altitude Calculator
Find the air pressure, temperature and density at any altitude up to 20 000 m (65 617 ft) using the ISA standard atmosphere model. Results are given in hPa, Pa, atm, and psi.
m
Altitude unit
88.7 % of sea-level pressure • 0.887 atm
- 1
Temperature at altitude
288.15 − 0.0065 × 1,000 m = 281.65 K - 2
Temperature ratio T / T₀
281.65 ÷ 288.15 = 0.977442 - 3
Pressure (Pa)
101 325 × 0.977442^5.2561 = 89,874.8 PaISA troposphere formula: P = P₀ × (T/T₀)^5.2561. - 4
Air pressure (hPa)
89,874.8 ÷ 100 = 898.7
How does this calculator work?
Using the ISA model, pressure in the troposphere is P = 101 325 × (1 − 0.0065 h / 288.15)^5.2561 Pa, falling from 1013 hPa at sea level to about 226 hPa at 11 km. Temperature drops 6.5 °C per km. Enter an altitude in metres or feet to get pressure in hPa, Pa, atm and psi, plus air temperature and density.
Formula
How this is calculated
This calculator uses the International Standard Atmosphere (ISA) — a model adopted by ICAO, aviation, and meteorology as the global reference for how pressure, temperature, and density vary with altitude. In the troposphere (sea level to 11 000 m) the temperature falls at a constant lapse rate of 6.5 K per kilometre: T(h) = 288.15 − 0.0065 × h. Pressure follows from the hydrostatic equation and the ideal-gas law, giving P = 101 325 × (T/288.15)^5.2561. Because the exponent equals gM/(RL) ≈ 5.2561, pressure drops faster than temperature.
Above 11 000 m the ISA enters the lower stratosphere, where temperature is constant at 216.65 K (−56.5 °C). Here pressure decays purely exponentially: P = P₁₁ × exp(−gM(h−11 000)/(R × 216.65)). Air density at any point follows from the ideal gas law: ρ = PM/(RT). This calculator covers the troposphere and lower stratosphere (0–20 km), which includes all civil aviation altitudes and most meteorological applications.
Real-world pressure differs from the ISA whenever weather systems, temperature inversions, or humidity are present. The ISA gives a useful standard reference but not a live reading — use a barometer or altimeter setting for real conditions.
Frequently asked questions
The relationship is non-linear because each thin layer of atmosphere must support all the air above it. As you climb, the overlying column becomes shorter and lighter, so pressure falls steeply. Temperature drops in the troposphere at a roughly constant lapse rate of 6.5 °C per km, which is slower relative to pressure.
At 10 700 m the ISA gives roughly 236 hPa — about 23 % of sea-level pressure. Aircraft cabins are pressurised to an equivalent of around 1800–2400 m (6 000–8 000 ft) so passengers breathe at 75–80 % of sea-level pressure.
Yes, but only slightly on the pressure scale. Humid air is less dense than dry air (water vapour replaces heavier N₂/O₂), so the ISA slightly overestimates density in humid conditions. Pilots use density altitude — the altitude in the standard atmosphere that matches the actual air density — to correct for temperature and humidity effects on aircraft performance.
TG we-Calculate Editorial Team. (2026). Air Pressure at Altitude Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/air-pressure-at-altitude-calculator
TG we-Calculate Editorial Team. "Air Pressure at Altitude Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/air-pressure-at-altitude-calculator.
TG we-Calculate Editorial Team, "Air Pressure at Altitude Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/air-pressure-at-altitude-calculator
@misc{wecalculate_air_pressure_at_altitude_calculator, title = {Air Pressure at Altitude Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/air-pressure-at-altitude-calculator}}, year = {2026}, note = {TG we-Calculate} }
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