Ideal gas relationship
ρ = p / (R x T)
R = 287.05 J/(kg x K)
T in kelvin
Standard atmosphere calculator
Air Density vs Altitude Calculator
Calculate International Standard Atmosphere air density from altitude, with pressure and temperature shown alongside the density result.
Instant ISA density solver
Enter altitude
Results update automatically using interpolated International Standard Atmosphere reference values.
Calculated result
Formulas
Air density vs altitude formulas used
Unit conversions
km = m / 1000
m = ft x 0.3048
lb/ft3 = kg/m3 x 0.062428
The calculator interpolates standard atmosphere pressure, temperature, and density values by altitude. For final design, verify against the governing atmosphere model, aircraft performance method, or site weather data.
Reference table
Air density by altitude table
| Altitude (km) | Altitude (ft) | Temperature (°C) | Pressure (kPa) | Density (kg/m3) | Density Ratio |
|---|---|---|---|---|---|
| 0 | 0 | 15.0 | 101.325 | 1.2250 | 1.000 |
| 1 | 3,281 | 8.5 | 89.875 | 1.1116 | 0.907 |
| 2 | 6,562 | 2.0 | 79.495 | 1.0065 | 0.822 |
| 3 | 9,843 | -4.5 | 70.108 | 0.9093 | 0.742 |
| 4 | 13,123 | -11.0 | 61.640 | 0.8194 | 0.669 |
| 5 | 16,404 | -17.5 | 54.020 | 0.7364 | 0.601 |
| 6 | 19,685 | -24.0 | 47.181 | 0.6601 | 0.539 |
| 7 | 22,966 | -30.5 | 41.061 | 0.5900 | 0.482 |
| 8 | 26,247 | -37.0 | 35.600 | 0.5258 | 0.429 |
| 9 | 29,528 | -43.5 | 30.742 | 0.4671 | 0.381 |
| 10 | 32,808 | -50.0 | 26.436 | 0.4135 | 0.338 |
| 11 | 36,089 | -56.5 | 22.632 | 0.3639 | 0.297 |
| 12 | 39,370 | -56.5 | 19.330 | 0.3108 | 0.254 |
| 15 | 49,213 | -56.5 | 12.045 | 0.1937 | 0.158 |
| 20 | 65,617 | -56.5 | 5.475 | 0.08891 | 0.073 |
| 25 | 82,021 | -51.6 | 2.511 | 0.04008 | 0.033 |
| 30 | 98,425 | -46.6 | 1.172 | 0.01841 | 0.015 |
| 40 | 131,234 | -22.1 | 0.287 | 0.003996 | 0.0033 |
| 50 | 164,042 | -2.5 | 0.0798 | 0.001027 | 0.00084 |
| 60 | 196,850 | -26.1 | 0.0203 | 0.0003097 | 0.00025 |
| 70 | 229,659 | -53.6 | 0.00463 | 0.00008283 | 0.000068 |
| 80 | 262,467 | -74.5 | 0.000886 | 0.00001846 | 0.000015 |
| 86 | 282,152 | -86.3 | 0.000373 | 0.00000696 | 0.0000057 |
Guide
How to use this altitude density calculator
- Enter the geometric altitude.
- Select meters, kilometers, or feet.
- Use the density, density ratio, pressure, and temperature results for early aerodynamic, HVAC, buoyancy, or atmospheric calculations.
Reference
What the results mean
Air density
Air density is mass per unit volume. It directly affects drag force, lift, mass flow rate, buoyancy, and fan or compressor performance.
Density ratio
Density ratio compares the calculated density to sea-level standard density. It is useful for quick altitude performance estimates.
Standard atmosphere
ISA values represent a reference atmosphere, not a weather forecast. Actual density depends on local pressure, temperature, and humidity.
Design use
Use altitude density values for aircraft performance, wind loading, natural ventilation, combustion air, CFD setup, and high-altitude equipment checks.
FAQ
Air density vs altitude questions
What is the air density at sea level?
In the International Standard Atmosphere, dry air density at sea level is approximately 1.225 kg/m3.
Why does air density decrease with altitude?
Air density decreases with altitude because atmospheric pressure falls as there is less air mass above the point being evaluated.
Can I use this for real weather conditions?
Use this page for standard atmosphere estimates. Real air density changes with local temperature, pressure, humidity, and weather conditions.
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