Calculator inputs
Formula used
This calculator supports two common atmosphere models. The lapse-rate formula works when temperature decreases with altitude. The isothermal formula works when temperature is treated as constant across the layer.
- h = altitude
- P = observed pressure
- P₀ = reference sea-level pressure
- T₀ or T = absolute temperature in kelvin
- L = temperature lapse rate
- R = universal gas constant
- g = gravitational acceleration
- M = molar mass of air
How to use this calculator
- Enter the observed barometric pressure from your instrument or dataset.
- Choose the same unit for both observed and reference pressure.
- Set a reference temperature and lapse rate that match your conditions.
- Select either the lapse-rate or isothermal atmosphere model.
- Pick the altitude output unit and press the convert button.
- Review the result, graph, and downloadable profile table.
Example data table
| Pressure (hPa) | Reference pressure (hPa) | Temperature (°C) | Lapse rate (K/km) | Estimated altitude (m) |
|---|---|---|---|---|
| 1013.25 | 1013.25 | 15 | 6.5 | 0 |
| 950 | 1013.25 | 15 | 6.5 | 540.4 |
| 900 | 1013.25 | 15 | 6.5 | 988.5 |
| 850 | 1013.25 | 15 | 6.5 | 1457.4 |
| 800 | 1013.25 | 15 | 6.5 | 1949.0 |
Frequently asked questions
1. What does this calculator estimate?
It estimates altitude from barometric pressure using standard atmospheric relationships. Results depend on the pressure reference, temperature assumption, lapse rate, and chosen model.
2. Why does lower pressure mean higher altitude?
Air pressure falls with height because less air remains above you. The atmosphere becomes thinner, so the measured force per unit area decreases as altitude increases.
3. Which reference pressure should I use?
Use local sea-level pressure when available. If you want a standard comparison, use 1013.25 hPa. A poor reference pressure can shift the altitude result noticeably.
4. When should I choose the lapse-rate model?
Choose the lapse-rate model when air temperature decreases with altitude across the layer. It matches many lower-atmosphere calculations and is a practical default.
5. When is the isothermal model useful?
Use the isothermal model when temperature is treated as constant through the evaluated layer. It is simpler and can be useful for narrow altitude ranges or theoretical comparisons.
6. Can the result be negative?
Yes. If observed pressure is higher than the chosen sea-level reference, the calculation returns a negative altitude, which represents a location below the reference level.
7. Why do meteorological and GPS altitudes differ?
Barometric altitude depends on atmospheric conditions and pressure calibration. GPS altitude depends on satellite geometry and geodetic models. They measure height differently, so differences are common.
8. How accurate is this method?
It can be very useful, but accuracy drops when weather changes, local pressure varies, or temperature assumptions are unrealistic. Better inputs generally produce better altitude estimates.