Altitude from Pressure Calculator

Estimate altitude from local and sea-level pressure using the standard atmosphere barometric formula, with optional temperature input.

Input

From the measured local pressure and the sea-level reference pressure, this computes altitude using the standard atmosphere barometric formula. Temperature is optional.

Local pressure P

hPa

Enter the pressure measured at your location.

Sea-level pressure P0

hPa

Reference sea-level pressure. The standard value is 1013.25 hPa.

Temperature (optional)

deg C

If left blank, the standard 15 degrees Celsius is used as the base temperature.

Result

Altitude

988.517225m

About 0.988517 km

Pressure ratio P / P0

0.888231

Base temperature

288.15 K

Computed with the barometric formula h = (T0 / L) × (1 − (P / P0)^(R·L/(g·M))), assuming a standard atmosphere.

How it works

Altitude is found with the standard atmosphere (ISA) barometric formula h = (T0 / L) × (1 − (P / P0)^(R·L/(g·M))).
Constants used: lapse rate L = 0.0065 K/m, gravity g = 9.80665 m/s^2, molar mass of dry air M = 0.0289644 kg/mol, gas constant R = 8.31446 J/(mol·K).
When no temperature is entered, the standard sea-level temperature of 15 degrees Celsius (288.15 K) is used as the base temperature. The exponent R·L/(g·M) is about 0.190263.
If the local pressure exceeds the sea-level pressure (for example below sea level), the input is treated as out of range.
Real air varies with temperature and humidity profiles, so the result is an estimate that assumes a standard atmosphere.

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