Altitude Pressure Calculator
Calculate atmospheric pressure at any altitude using the international barometric formula. Useful for aviation, hiking, and altitude sickness planning.
How to use this tool
- Enter your altitude in metres above sea level.
- The calculator uses the international standard atmosphere barometric formula to compute pressure.
- Results are shown in hectopascals (hPa), PSI, and as a percentage of sea-level pressure.
Calculate the atmospheric pressure at any altitude above sea level using the international standard barometric formula.
Formula
P(h) = 1013.25 × (1 − 2.2557 × 10−5 × h)5.25588 hPa
P (psi) = P(h) × 0.0145038
% of sea-level = P(h) ÷ 1013.25 × 100
How it works
This calculator applies the International Standard Atmosphere (ISA) barometric formula for the troposphere to compute atmospheric pressure at a given altitude in metres. The formula models the decrease in pressure as a power-law function of altitude, assuming a standard temperature lapse rate of 6.5 K/km and sea-level pressure of 1013.25 hPa. Results are accurate for altitudes up to approximately 11,000 m (the tropopause); above that, a different formula applies. Actual pressure on any given day will deviate from the ISA model due to weather.
Worked example
Worked example
- Altitude = 1000 m.
- P = 1013.25 × (1 − 2.2557 × 10−5 × 1000)5.25588.
- Inner term = 1 − 0.022557 = 0.977443.
- P = 1013.25 × 0.9774435.25588 ≈ 1013.25 × 0.8872 ≈ 898.75 hPa.
- In psi: 898.75 × 0.0145038 ≈ 13.03 psi; % of sea-level = 898.75 ÷ 1013.25 × 100 ≈ 88.70%.
Pressure = 898.75 hPa (13.03 psi); 88.70% of sea-level pressure
Key terms
- International Standard Atmosphere (ISA)
- A model of how atmospheric pressure, temperature, and density vary with altitude, defined by ICAO and used as a reference for aviation and engineering.
- Hectopascal (hPa)
- A unit of pressure equal to 100 pascals and numerically identical to the millibar (mbar); the standard unit for atmospheric pressure in meteorology and aviation.
- Tropopause
- The boundary between the troposphere and stratosphere, at approximately 11 km altitude in the ISA, above which the temperature stops decreasing with height.
- Altitude sickness (AMS)
- Acute mountain sickness caused by reduced partial pressure of oxygen at altitude; symptoms typically begin above 2500 m.
- Barometric formula
- The mathematical expression relating atmospheric pressure to altitude, derived from the hydrostatic equation and an assumed temperature profile.
Frequently asked questions
- How does altitude affect air pressure?
- Atmospheric pressure decreases with altitude because there is less air above. At 1000 m, pressure is about 89% of sea level. At 5000 m (similar to high-altitude treks), pressure drops to around 54% of sea level.
- What is the barometric formula?
- The standard barometric formula is P = 1013.25 × (1 − 2.2557×10⁻⁵ × h)^5.25588, where h is altitude in metres and P is pressure in hPa. It is valid up to about 11,000 m.
- How does altitude affect the human body?
- At altitudes above 2400 m (8000 ft), reduced oxygen availability can cause altitude sickness (AMS). Above 5500 m, acclimatisation becomes very difficult and supplemental oxygen may be needed.