Atmospheric Pressure at Altitude Calculator

Atmospheric pressure is caused by the weight of air above a given point. As altitude increases, there is less air mass above, so the gravitational force pressing down is smaller. This causes pressure to drop in an approximately exponential manner as you ascend.

This calculator uses the barometric (hypsometric) formula: P = P₀ × exp(−gM(h − h₀) / RT), where P₀ is sea-level pressure, g is gravitational acceleration (9.80665 m/s²), M is the molar mass of dry air (0.0289644 kg/mol), h is the target altitude, h₀ is the reference altitude, R is the universal gas constant (8.31446 J/mol·K), and T is the temperature in Kelvin.

Standard atmospheric pressure at sea level is defined as 1013.25 hPa (millibars), which equals 101,325 Pascals, 29.9213 inHg, or 14.696 psi. This is used as the baseline reference in most aviation, meteorological, and scientific applications.

Convert your altitude to metres, then apply the exponential barometric formula using your sea-level pressure and temperature in Kelvin. The result gives the absolute atmospheric pressure at that elevation. This calculator handles all unit conversions and the formula automatically.

Temperature influences air density: warmer air is less dense, so the pressure decreases more slowly with altitude; colder air is denser, and pressure drops more steeply. The barometric formula includes temperature to account for this effect. Enter the actual temperature at your altitude for the most accurate result.

Pressure altitude is the altitude in the International Standard Atmosphere (ISA) that corresponds to a given pressure, regardless of the actual temperature. Geometric (or true) altitude is the actual height above sea level. In aviation, pressure altitude is used to standardize altimeter readings and calculate aircraft performance.

Under standard conditions, atmospheric pressure is roughly half of sea-level pressure at approximately 5,500 metres (about 18,000 feet). This is sometimes called the 'half-pressure altitude' and is significant for aviation and high-altitude physiology.

Enter your altitude and select the unit (metres, feet, km, or miles). Input the sea-level pressure (default 1013.25 hPa) and temperature at that altitude (default 15°C). Choose your preferred output pressure unit, and the calculator instantly displays the air pressure at your specified altitude along with a reference table.