Calculate temperature at any altitude using ISA lapse rate. Find atmospheric pressure, air density, and boiling point changes for aviation and mountaineering.
The **Altitude Temperature Calculator** determines air temperature at any altitude using the International Standard Atmosphere (ISA) lapse rate model. As you ascend through the troposphere, temperature drops at approximately 6.5°C per 1,000 meters (about 3.6°F per 1,000 feet) — a relationship critical for pilots, mountaineers, meteorologists, and engineers.
This calculator goes beyond simple temperature estimation. It also computes atmospheric pressure, air density, water boiling point, and effective oxygen levels at your specified altitude. Pilots use these values for performance calculations, climbers need them for altitude sickness assessment, and engineers rely on them for engine and HVAC design at elevation.
The ISA model divides the atmosphere into layers — the troposphere (surface to ~11 km) where temperature decreases linearly, the tropopause where it stabilizes, and the stratosphere where it gradually increases. Enter your altitude and ground conditions to get comprehensive atmospheric data instantly. Check the example with realistic values before reporting.
This calculator is essential for anyone working with altitude-dependent conditions — from pilots computing density altitude to mountaineers assessing cold exposure risk to engineers designing systems that operate at elevation.
Instead of memorizing lapse rates and manually computing pressure ratios, get instant results for any altitude with supporting data including air density, boiling point, and oxygen levels — all critical for safety and performance planning.
T(h) = T₀ − L × h (for h ≤ 11,000 m) Where: - T(h) = temperature at altitude h - T₀ = ground-level temperature (ISA standard: 15°C) - L = lapse rate = 6.5°C per 1,000 m (ISA standard) - h = altitude in meters Pressure: P = 1013.25 × (1 − 2.25577 × 10⁻⁵ × h)^5.25588 (hPa) Density: ρ = 1.225 × (1 − 2.25577 × 10⁻⁵ × h)^4.25588 (kg/m³)
Result: -4.5°C at 3,000 m
Starting at 15°C sea level, the temperature decreases by 6.5°C per km. At 3 km: 15 − (6.5 × 3) = −4.5°C. Pressure drops to ~701 hPa and water boils at ~90°C.
The ISA is a reference model established by ICAO that defines standard conditions for the atmosphere from sea level to 80 km. At sea level, ISA specifies 15°C, 1013.25 hPa pressure, and 1.225 kg/m³ air density. The tropospheric lapse rate of 6.5°C/km provides a baseline that pilots, engineers, and scientists worldwide use for calculations.
In reality, atmospheric conditions constantly deviate from ISA. A "hot day" at an airport might show ISA+15, meaning temperatures are 15°C above standard — significantly affecting aircraft takeoff performance by reducing air density and therefore lift and engine thrust.
As altitude increases, the decreasing air pressure reduces the partial pressure of oxygen available for breathing. At 2,500 m, most people notice mild effects. At 3,500 m, altitude sickness becomes common without acclimatization. Above 8,000 m — the "death zone" — human survival without supplemental oxygen is limited to hours.
The calculator shows effective oxygen percentage, which represents the equivalent sea-level oxygen concentration. This metric is widely used in aviation medicine and mountaineering to assess hypoxia risk at altitude.
**HVAC Systems:** Air conditioning and ventilation systems at altitude must be sized differently because air density affects heat transfer. A system designed for sea level will underperform at 2,000 m without adjustment.
**Combustion Engines:** Internal combustion engines lose approximately 3% power per 300 m of altitude gain due to decreased air density. Turbocharged engines partially compensate, but the temperature and pressure data from this calculator are essential for accurate performance modeling.
**Construction:** Concrete curing, paint drying, and adhesive bonding are all affected by temperature and pressure at altitude. Engineers working on high-altitude projects need these environmental parameters for specification compliance.
The International Standard Atmosphere defines a lapse rate of 6.5°C per 1,000 meters (or 1.98°C per 1,000 feet) in the troposphere, from sea level to about 11 km altitude.
At the tropopause (~11 km), the ozone layer begins absorbing UV radiation, which heats the stratosphere. Temperature remains roughly constant or increases slightly.
The ISA is a model for average conditions. Real temperatures vary due to weather, season, latitude, and time of day. Actual lapse rates range from 4-10°C/km depending on moisture and conditions.
Aircraft performance (lift, engine power, true airspeed) depends heavily on air density, which is determined by temperature and pressure at altitude. ISA deviations affect flight planning significantly.
Water boils at 37°C (body temperature) at about 19,200 m altitude — this is the Armstrong limit, above which unprotected humans cannot survive. Use this as a practical reminder before finalizing the result.
While the percentage of oxygen (20.9%) stays constant, the partial pressure decreases with altitude. At 5,500 m, effective oxygen is roughly half of sea level, causing altitude sickness in unacclimatized people.