Altitude & Pressure Calculator.

Convert between altitude and atmospheric pressure using the International Standard Atmosphere (ISA) model. Also shows temperature and air density at any altitude.

Altitude

Quick Reference Altitudes

Location	Altitude	Pressure	ISA Temp
Sea Level	0 m	1013.25 hPa	15.0°C
Denver, CO	1609 m	835 hPa	4.6°C
Mont Blanc	4808 m	555 hPa	-16.3°C
Cruising Altitude	10000 m	265 hPa	-50.0°C
Mount Everest	8849 m	315 hPa	-42.5°C

How to convert altitude and air pressure

Choose whether you are entering an altitude or a pressure.
Enter the value.
Read the converted figure, plus the standard temperature at that height.
Remember these are International Standard Atmosphere values — real weather shifts them daily.

About Altitude & Pressure

As altitude increases, atmospheric pressure decreases because there is less air above pressing down. The relationship is modelled by the International Standard Atmosphere (ISA), which defines standard conditions at each altitude layer.

In the troposphere (0–11 km), temperature decreases by 6.5°C per 1000 m (the lapse rate). At the tropopause (~11 km), temperature stabilises at −56.5°C. This calculator uses ISA troposphere values only (valid to 11,000 m / 36,089 ft).

Applications include aviation (altimetry), meteorology, hiking and mountaineering planning, and engineering calculations involving air density.

Frequently Asked Questions

How does air pressure change with altitude?

It falls roughly exponentially. In the International Standard Atmosphere, pressure is 1,013.25 hPa at sea level, 898.7 hPa at 1,000 m, 795 hPa at 2,000 m, 540 hPa at 5,000 m, and about 314 hPa at the height of Everest (8,849 m), less than a third of sea level.

What is the International Standard Atmosphere?

A reference model of how pressure, temperature and density vary with height: 15 °C and 1,013.25 hPa at sea level, with temperature falling 6.5 °C per 1,000 m up to 11 km. Aircraft altimeters, engine ratings and this calculator all use it. Real weather departs from it by a few per cent.

How cold is it at altitude?

In the standard atmosphere temperature drops 6.5 °C per 1,000 m, so 15 °C at sea level becomes 8.5 °C at 1,000 m, 2 °C at 2,000 m and −17.5 °C at 5,000 m. Actual lapse rates vary with humidity and weather.

Why does this calculator stop at 11,000 m?

Because that is where the troposphere ends. Above about 11 km temperature stops falling and holds near −56.5 °C, so the formula used below it no longer applies. The calculator covers 0–11,000 m (0–36,089 ft), which includes every inhabited place and most flight levels.

Sources · Reviewed 24 September 2026

ICAO Doc 7488, Manual of the ICAO Standard Atmosphere (troposphere, 0–11 km)