MasterTool

Air Pressure at Altitude Calculator

Calculate air pressure at altitude instantly in your browser — the published formula, worked locally with no data sent anywhere.

Loading calculator…

What this tool does

Calculate air pressure at altitude instantly in your browser — the published formula, worked locally with no data sent anywhere. This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.

How to use the Air Pressure at Altitude Calculator

  1. Enter or select altitude in ft.
  2. Read the calculated result; change any measurement to compare alternatives.

Formula

ISA barometric formula: P = 1013.25 × (1 − 2.25577×10⁻⁵ × h)^5.25588 hPa, with h in metres; standard temperature at altitude = 15 − 6.5 °C per 1000 m.
alt
Altitude (ft, before metric conversion)

This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.

Worked example

For air pressure at altitude calculator, the following measurements illustrate the exact method: Altitude: 5000.

Inputs

  • Altitude5000 ft

Result

  • Standard pressure (hPa)843.07
  • Standard pressure (inHg)24.9
  • Standard pressure (psi)12.23
  • Pressure as % of sea level83.2
  • ISA temperature at this altitude (°C)5.09
  • Altitude (m)1,524

Results explained

Standard pressure (hPa)
Standard pressure (hPa) from the formula above. This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.
Standard pressure (inHg)
Standard pressure (inHg) from the formula above. This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.
Standard pressure (psi)
Standard pressure (psi) from the formula above. This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.
Pressure as % of sea level
Pressure as % of sea level from the formula above. This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.
ISA temperature at this altitude (°C)
ISA temperature at this altitude (°C) from the formula above. This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.
Altitude (m)
Altitude (m) from the formula above. This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.

Frequently asked questions

ISA barometric formula: P = 1013.25 × (1 − 2.25577×10⁻⁵ × h)^5.25588 hPa, with h in metres; standard temperature at altitude = 15 − 6.5 °C per 1000 m.

This is the International Standard Atmosphere model — the pressure on a 'standard day'. Real pressure at a given altitude varies with weather systems by several percent; altimeters are calibrated against this same model.

An altimeter is just a barometer reading this ISA table backwards. When a low-pressure system moves in, the air at your true altitude has the pressure the model expects higher up, so the altimeter over-reads until you reset it to the local altimeter setting.

Every field is labelled with its unit — enter values in exactly the labelled unit and read the result in the labelled output unit. Fields with a unit symbol also support the site-wide imperial/metric switch, which converts before the formula runs.

It uses double-precision arithmetic and the published constants and formulas named on this page. The last displayed digit may be rounded, and real conditions can differ from the idealized model described in the assumptions.

Yes. Every calculation runs entirely in your browser; nothing you enter is uploaded, stored or shared.