Barometric relationship
p decreases with altitude
p = rho x R x T
R = 287.05 J/(kg x K)
Standard atmosphere calculator
Air Pressure vs Altitude Calculator
Calculate International Standard Atmosphere pressure from altitude, with temperature and density shown alongside the pressure result.
Instant ISA pressure solver
Enter altitude
Results update automatically using interpolated International Standard Atmosphere reference values.
Calculated result
Formulas
Air pressure vs altitude formulas used
Unit conversions
Pa = kPa x 1000
psi = kPa x 0.145038
m = ft x 0.3048
The calculator interpolates International Standard Atmosphere pressure values by altitude. Actual atmospheric pressure varies with weather, latitude, season, and local elevation conditions.
Reference table
Air pressure by altitude table
| Altitude (km) | Altitude (ft) | Pressure (kPa) | Pressure (kPa) | Density (kg/m3) |
|---|---|---|---|---|
| 0 | 0 | 101.325 | 101.325 | 1.225 |
| 1 | 3,281 | 89.875 | 89.875 | 1.1116 |
| 2 | 6,562 | 79.495 | 79.495 | 1.0065 |
| 3 | 9,843 | 70.108 | 70.108 | 0.9093 |
| 4 | 13,123 | 61.64 | 61.64 | 0.8194 |
| 5 | 16,404 | 54.02 | 54.02 | 0.7364 |
| 6 | 19,685 | 47.181 | 47.181 | 0.6601 |
| 7 | 22,966 | 41.061 | 41.061 | 0.59 |
| 8 | 26,247 | 35.6 | 35.6 | 0.5258 |
| 9 | 29,528 | 30.742 | 30.742 | 0.4671 |
| 10 | 32,808 | 26.436 | 26.436 | 0.4135 |
| 11 | 36,089 | 22.632 | 22.632 | 0.3639 |
| 12 | 39,370 | 19.33 | 19.33 | 0.3108 |
| 15 | 49,213 | 12.045 | 12.045 | 0.1937 |
| 20 | 65,617 | 5.475 | 5.475 | 0.08891 |
| 25 | 82,021 | 2.511 | 2.511 | 0.04008 |
| 30 | 98,425 | 1.172 | 1.172 | 0.01841 |
| 40 | 131,234 | 0.287 | 0.287 | 0.003996 |
| 50 | 164,042 | 0.0798 | 0.0798 | 0.001027 |
| 60 | 196,850 | 0.0203 | 0.0203 | 0.0003097 |
| 70 | 229,659 | 0.00463 | 0.00463 | 8.283E-5 |
| 80 | 262,467 | 0.000886 | 0.000886 | 1.846E-5 |
| 86 | 282,152 | 0.000373 | 0.000373 | 6.96E-6 |
Guide
How to use this calculator
- Enter the geometric altitude.
- Select meters, kilometers, or feet.
- Use the interpolated standard-atmosphere result for early aerospace, HVAC, fluid mechanics, or thermodynamic checks.
Reference
What the results mean
Air pressure
Air pressure is the force per unit area exerted by the weight of the atmosphere above a point.
Altitude effect
Pressure falls rapidly with altitude because there is less air mass above the measurement point.
Engineering use
Use pressure-altitude values for aircraft performance, high-altitude HVAC, combustion air, instrumentation, and compressible-flow estimates.
Standard atmosphere
ISA is a reference model. Actual pressure depends on weather systems and local atmospheric conditions.
FAQ
Air pressure vs altitude questions
What is standard air pressure at sea level?
Standard sea-level pressure is 101.325 kPa, or 101,325 Pa.
What happens to air pressure as altitude increases?
Air pressure decreases as altitude increases because less atmosphere remains above the point.
Is ISA pressure the same as local weather pressure?
No. ISA pressure is a reference model; local weather pressure can differ significantly.
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