Altitude to air pressure converter
Convert an altitude to the standard air pressure there, or a pressure to its altitude, with the boiling point of water at that height.
Nothing on our list is smaller: Denver, the “Mile High City” is 1.01× higher. Standard pressure there is 835.2 hPa (82.43 % of sea level), and water boils at 94.69 °C.
What it means
How high is that?
International Standard Atmosphere (ISO 2533), from −610 m to 20 km. Real pressure varies with weather by a few percent; temperature is the standard one, valid up to 11 km.
Every unit
That altitude in every unit
Learn
Three things worth knowing
-
Half the air at 5.5 km
Pressure halves about every 5.5 km: 1013 hPa at sea level, 505 hPa at 5,500 m, 250 hPa at 10,400 m. Near the ground it drops about 1 hPa per 8 m.
-
Torricelli’s tube
Evangelista Torricelli balanced the air with a column of mercury in 1643. Pascal had it carried up the Puy de Dôme in 1648, and the column fell: air has weight.
-
Altimeters read pressure
An aircraft altimeter measures pressure and assumes the standard atmosphere. On a cold or low-pressure day you are lower than it says: “high to low, look out below”.
Shortcuts
Popular altitude conversions
Background
About the standard atmosphere
Air pressure falls as you climb because there is less air above you. The International Standard Atmosphere fixes an average: 1013.25 hPa and 15 °C at sea level, cooling 6.5 °C per kilometer up to 11 km. Altimeters, aircraft performance charts and engineers all use it.
Lower pressure also lowers the boiling point of water: about 95 °C in Denver and 70 °C on top of Everest, which is why pasta takes longer in the mountains.