Calculate atmospheric pressure, temperature, and air density at any altitude using the International Standard Atmosphere (ISA) model. Supports humidity correction.
Atmospheric pressure decreases with altitude because there is less air above pressing down. The International Standard Atmosphere (ISA) defines how pressure, temperature, and density vary with height: in the troposphere (0–11 km), temperature drops at 6.5°C per km and pressure follows a power-law profile; in the lower stratosphere (11–20 km), temperature is constant and pressure drops exponentially.
This calculator implements the ISA barometric formula for altitudes from sea level to 47 km. You can adjust the sea-level pressure for current weather conditions, apply temperature deviations from the standard profile, and include relative humidity for a moist-air density correction. The outputs include pressure in six unit systems, temperature, air density, and the altitude-corrected boiling point of water.
Pilots use altimeter settings (inHg or hPa) to convert pressure to altitude. Engineers need air density for drag and lift calculations. Hikers and climbers want to know the boiling point of water at camp altitude. This tool serves all those needs in a single interface.
Whether you are a pilot checking density altitude, an engineer computing drag at altitude, or a mountaineer planning a camp stove, this calculator gives accurate atmospheric properties at any height using the internationally accepted ISA model. The note above highlights common interpretation risks for this workflow. Use this guidance when comparing outputs across similar calculators. Keep this check aligned with your reporting standard.
Troposphere (h ≤ 11 000 m): T = T_b + L_b × h P = P_b × (T/T_b)^(−gM/RL_b) Stratosphere (11 000 < h ≤ 20 000 m): T = 216.65 K (constant) P = P_11 × exp(−gM(h−11000)/(RT)) Where: • T_b = 288.15 K, P_b = 101 325 Pa • L_b = −0.0065 K/m, g = 9.80665 m/s² • M = 0.0289644 kg/mol, R = 8.31447 J/(mol·K)
Result: 83.5 kPa (0.824 atm)
At 1 609 m in ISA conditions, T = 288.15 − 0.0065 × 1609 = 277.6 K. P = 101 325 × (277.6/288.15)^5.256 ≈ 83 500 Pa. Pressure is about 82% of sea level.
Use consistent units, verify assumptions, and document conversion standards for repeatable outcomes.
Most mistakes come from mixed standards, rounding too early, or misread labels. Recheck final values before use. ## Practical Notes
Use this for repeatability, keep assumptions explicit. ## Practical Notes
Track units and conversion paths before applying the result. ## Practical Notes
Use this note as a quick practical validation checkpoint. ## Practical Notes
Keep this guidance aligned to the calculator’s expected inputs. ## Practical Notes
Use as a sanity check against edge-case outputs. ## Practical Notes
Capture likely mistakes before publishing this value. ## Practical Notes
Document expected ranges when sharing results.
Near sea level, pressure drops roughly 12 kPa per 1 000 m (about 12%). The rate decreases with altitude because the atmosphere thins exponentially, not linearly.
Boiling occurs when vapor pressure equals atmospheric pressure. Lower atmospheric pressure means less vapor pressure is needed, so water boils at a lower temperature — roughly 3.4°C less per 1 000 m.
ISA deviation (ISA±°C) is the difference between actual temperature and the standard atmosphere temperature at that altitude. Pilots report ISA+10 or ISA−5 to describe non-standard conditions.
Water vapor (M = 0.018 kg/mol) is lighter than dry air (M = 0.029 kg/mol). Humid air is therefore slightly less dense than dry air at the same pressure and temperature, affecting aircraft performance.
An altimeter is a calibrated barometer. It measures ambient pressure and converts it to an altitude using the ISA profile. Pilots set the local sea-level pressure (QNH) to get accurate altitude readings.
ISA is an idealized average. Real atmospheric conditions vary with weather, latitude, and season. For precise work, use radiosondes or numerical weather prediction data.