ISA Barometric Formula · Elevation Correction
Barometric pressure, altitude corrections, and standard conditions
Atmospheric pressure decreases with increasing elevation following the ICAO International Standard Atmosphere barometric formula. At sea level, standard pressure is 14.696 psia, dropping to approximately 12.1 psia at 5,280 ft (Denver) and 10.1 psia at 10,000 ft.
Atmospheric pressure is essential for converting gauge pressure readings to absolute pressure, which is required for gas volume corrections, flow calculations, and equipment sizing. Incorrect atmospheric pressure assumptions can cause significant measurement errors at higher elevations.
The ISA barometric formula calculates pressure as P = P₀ × [1 − (L × h / T₀)]^5.2558, where P₀ is sea level pressure (14.696 psia), h is elevation in feet, T₀ is 518.67 °R, and L is the temperature lapse rate of 0.00357 °R/ft. It is valid for the troposphere up to 36,089 ft.