Altitude Temperature Calculator — ISA Standard Atmosphere
Find the temperature, pressure, and air density at any altitude from sea level to 32,000 m (about 105,000 ft) using the International Standard Atmosphere model — the same model used in aviation, meteorology, and aerospace engineering.
Altitude unit
m
International Standard Atmosphere temperature at the entered altitude
- 1
Lapse rate × altitude
0.0065 × 3,000 = 19.5 - 2
ISA temperature (troposphere)
15 − 19.5 = -4.5Temperature drops 6.5 °C per 1,000 m in the troposphere.
How does this calculator work?
The ISA model gives T = 15 − 0.0065 × h °C in the troposphere (0–11 km), then −56.5 °C constant through the tropopause (11–20 km), rising again in the lower stratosphere. Pressure and air density follow from the hydrostatic equation and ideal gas law. Real conditions can differ by ±20 °C from these standard values.
Formula
How this is calculated
The International Standard Atmosphere (ISA, ISO 2533:1975) defines how temperature, pressure, and density vary with altitude under a set of globally averaged conditions. In the troposphere (sea level to 11,000 m), temperature falls at a constant lapse rate of 6.5 °C per kilometre, from +15 °C at sea level to −56.5 °C at the tropopause. Between 11,000 m and 20,000 m (the isothermal tropopause), temperature remains constant at −56.5 °C. In the lower stratosphere (20,000–32,000 m) it begins rising at 1 °C per kilometre.
Pressure follows from the hydrostatic equation and the ideal gas law. In the troposphere the pressure formula is P = 101325 × (T/288.15)^5.2561 Pa; in the isothermal zone it decays exponentially. Air density is then ρ = P / (R_air × T_K), where R_air = 287.058 J/(kg·K) and T_K is in kelvin.
The ISA is a statistical average — real atmospheric temperatures deviate by ±20 °C or more depending on latitude, season, and weather. It is used as a reference baseline, not a forecast. This calculator does not model wind, humidity, or ozone effects.
Frequently asked questions
In the troposphere, rising air expands adiabatically as pressure drops, losing energy — the dry adiabatic lapse rate is about 9.8 °C/km. The ISA uses the average (moist) environmental lapse rate of 6.5 °C/km, which balances atmospheric mixing and radiation.
The ISA tropopause starts at 11,000 m (36,089 ft), where the temperature is −56.5 °C (−69.7 °F / 216.65 K) and remains constant up to 20,000 m. This is why cruising jet aircraft (at ≈ 35,000–40,000 ft) experience near-constant −57 °C outside.
The ISA is a reference standard, not a forecast. Real-world temperatures differ by ±10–20 °C depending on latitude, time of year, and weather. Use actual radiosonde (weather balloon) data for precision applications such as aircraft performance calculations.
TG we-Calculate Editorial Team. (2026). Altitude Temperature Calculator — ISA Standard Atmosphere [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/altitude-temperature-calculator
TG we-Calculate Editorial Team. "Altitude Temperature Calculator — ISA Standard Atmosphere." TG we-Calculate. 2026. https://we-calculate.com/calculator/altitude-temperature-calculator.
TG we-Calculate Editorial Team, "Altitude Temperature Calculator — ISA Standard Atmosphere," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/altitude-temperature-calculator
@misc{wecalculate_altitude_temperature_calculator, title = {Altitude Temperature Calculator — ISA Standard Atmosphere}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/altitude-temperature-calculator}}, year = {2026}, note = {TG we-Calculate} }
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