ISA Atmosphere Properties Calculator
The complete standard-atmosphere row for any altitude: temperature, pressure, density, speed of sound and the δ/σ/θ ratios — troposphere and stratosphere both.
Both layers modeled honestly: the linear-lapse troposphere to 11 km and the isothermal stratosphere above it with exponential pressure decay — the same two-regime model inside every air-data computer and performance code.
Formula
⚠️ For planning and education only. Weight & balance must be computed from YOUR aircraft's actual empty weight, arm and current equipment list, and verified against the POH/AFM envelope before flight.
The complete standard-atmosphere row for any altitude: temperature, pressure, density, speed of sound and the δ/σ/θ ratios — troposphere and stratosphere both.
About ISA Atmosphere Properties Calculator
One altitude in, the whole standard-atmosphere row out: temperature, pressure in hectopascals, density in kg/m³, the local speed of sound, and the three normalized ratios engineers actually compute with. Unlike the simple troposphere-only formulas scattered online, this implements both ISA regimes — linear lapse to 11 km, then the isothermal stratosphere's exponential pressure decay — so FL450 queries return physics, not extrapolation error.
How to use ISA Atmosphere Properties Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula troposphere: T linear, p = p₀(T/T₀)^5.2559; stratosphere: T = 216.65 K, p exponential decay substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use ISA Atmosphere Properties Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula troposphere: T linear, p = p₀(T/T₀)^5.2559; stratosphere: T = 216.65 K, p exponential decay with sources cited on the page
- ✓Both layers modeled honestly: the linear-lapse troposphere to 11 km and the isothermal stratosphere above it with exponential pressure decay — the same two-regime model inside every air-data computer and performance code.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Why does the pressure formula change at 11 km?+
The hydrostatic equation integrates differently depending on the temperature profile: with T falling linearly (troposphere) it yields the power law (T/T₀)^5.2559; with T constant (stratosphere) it yields a pure exponential decay with a 6,340 m scale height. Same physics, two solutions — the kink at 36,089 ft is visible in every plotted sounding.
What fraction of the atmosphere is below an airliner?+
Pressure is the direct answer, since it measures the weight of air above: at FL300 the standard pressure is 300.9 hPa — 70% of the atmosphere's mass lies below you. At FL400 it's 81%. The 'thin air up there' is literal: cruise flight happens above two-thirds of all the air there is.
How accurate is ISA-1976 against the real atmosphere?+
As a climatological mid-latitude average, remarkably good: real monthly means deviate a few percent in density at most levels. Day to day, deviations of ±5% density and ±20 °C are routine — which is the point: ISA is the ruler, the deviation tools measure the day. For engineering (drag, performance, ballistics) ISA plus a deviation model covers nearly every use.
What's geopotential altitude in the input label?+
Altitude measured in gravity-adjusted metres — the variable the standard atmosphere's equations are actually written in. It differs from geometric (tape-measure) height by under 0.5% below 20 km, because g weakens slightly with height. Aviation altimetry, this calculator and ISA tables all speak geopotential; only space-adjacent work needs the distinction.
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