Barometric Pressure to Altitude
Estimate altitude above sea level from atmospheric pressure using the International Standard Atmosphere (ISA) barometric formula.
Results
What is it?
The barometric formula uses the relationship between atmospheric pressure and altitude to estimate elevation. The ISA (International Standard Atmosphere) model assumes a standard temperature lapse rate of 6.5 degrees C per 1,000 m. Pressure at sea level is 1013.25 hPa; at 5,500 m it is roughly half that (~540 hPa).
How to use
Enter the pressure reading from your barometer, altimeter, or weather station. Enter the current sea-level pressure (available from local weather services or aviation QNH). The result is your estimated altitude above sea level.
Example scenario
You measure 900 hPa on a mountain hike with sea-level pressure at 1013.25 hPa: altitude is approximately 1,000 m (3,281 ft). At 800 hPa you would be at approximately 1,949 m ? consistent with a high Alpine pass.
Pro tip
Always calibrate your altimeter at a known elevation ? pressure changes with weather, not just altitude. A 1 hPa change equals approximately 8 m of altitude at sea level. In aviation, setting QNH (sea-level pressure) gives altitude above sea level; QFE (aerodrome pressure) gives height above the airfield.