Temperature at Altitude Calculator

Calculate air temperature at a given altitude using the standard atmosphere lapse-rate formula, T = T0 − L×h, with results in Celsius, Fahrenheit, and Kelvin.

Quick Facts

Formula
T = T0 − L×h (troposphere, ISA model)
T0 is sea-level temperature, L is the lapse rate, h is altitude.
Standard lapse rate
6.5°C per 1,000 m
The ICAO Standard Atmosphere average, valid up to the tropopause (~11 km).

Your Results

Calculated
Temperature at altitude
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Degrees Celsius (°C)
In Fahrenheit
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Degrees Fahrenheit (°F)
In Kelvin
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Absolute temperature (K)
Atmospheric layer
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ISA model region

Ready

Set altitude, sea-level temperature, and lapse rate, then press Calculate.

Understanding Temperature at Altitude

Air gets colder as you climb — that is one of the most reliable patterns in the atmosphere. This calculator applies the International Standard Atmosphere (ISA) model, the reference model used in aviation, meteorology, and engineering, to estimate the temperature at a given altitude from a sea-level starting temperature and a lapse rate.

The formula

Within the troposphere (roughly the lowest 11 km / 36,089 ft of the atmosphere), temperature falls in a straight line as altitude increases:

  • T = T0 − L × h
  • T0 is the sea-level (h = 0) temperature.
  • L is the lapse rate, the rate temperature falls per unit of altitude — the ISA standard value is 6.5°C per 1,000 m.
  • h is altitude above sea level.

Above the tropopause (about 11 km) and up to roughly 20 km, the ISA model treats the lower stratosphere as isothermal — temperature stays essentially constant near −56.5°C rather than continuing to fall. This calculator applies the linear formula below 11 km and holds the tropopause temperature constant above it.

Standard atmosphere reference values

  • Sea-level standard temperature: 15°C (59°F, 288.15 K).
  • Standard lapse rate: 6.5°C per 1,000 m (about 3.57°F per 1,000 ft) in the troposphere.
  • Tropopause altitude: about 11,000 m (36,089 ft), where standard temperature is −56.5°C (216.65 K).

Why temperature drops with altitude

As altitude increases, air pressure and density decrease. Rising air expands and cools, and the atmosphere is heated mainly from below (by the sun-warmed ground and ocean), so the effect weakens with height. The 6.5°C/1,000 m figure is an average of many real-world soundings and is close to, but not identical to, the dry adiabatic lapse rate (about 9.8°C/1,000 m) that describes a single unsaturated air parcel rising on its own.

Frequently Asked Questions

What is the standard temperature lapse rate?
In the International Standard Atmosphere (ISA) model, temperature falls at an average of 6.5°C per 1,000 meters (about 3.57°F per 1,000 feet) within the troposphere, roughly the lowest 11 km of the atmosphere. This environmental lapse rate is a global average; real weather conditions, humidity, and season can push the local rate higher or lower.
What formula does this calculator use?
It uses the standard-atmosphere linear lapse-rate formula T = T0 − L×h, where T0 is the sea-level temperature, L is the lapse rate, and h is altitude. This applies in the troposphere, below about 11 km (36,089 ft). Above that tropopause, the ISA model treats temperature as roughly constant up to about 20 km, which is how this calculator handles higher altitudes.
Why does temperature stop falling above about 11 km?
That altitude marks the tropopause, the boundary between the troposphere and the stratosphere. In the standard atmosphere model, the lower stratosphere (about 11-20 km) is treated as isothermal, holding near −56.5°C, because the convection and pressure effects that cool the troposphere no longer dominate there.
Does this account for humidity or real weather conditions?
No. The calculator uses the idealized ISA model, a fixed global average used in aviation, engineering, and physics education. Actual temperature at a given altitude varies with weather systems, humidity, latitude, and season, and can even increase with height near the ground during a temperature inversion.

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