Barometric Pressure–Altitude Converter
Convert barometric pressure and altitude instantly using standard atmosphere equations. Choose units enter pressure or elevation and get results in meters feet hPa and inHg. Export a CSV or PDF report for records and sharing.
Developed by: Nohman Habib
Example Data
| Mode | Input | Sea Level Pressure | Output (Approx.) |
|---|---|---|---|
| Pressure → Altitude | 900 hPa | 1013.25 hPa | ≈ 988 m (≈ 3242 ft) |
| Pressure → Altitude | 800 hPa | 1013.25 hPa | ≈ 1949 m (≈ 6394 ft) |
| Altitude → Pressure | 1500 m | 1013.25 hPa | ≈ 845 hPa (≈ 24.96 inHg) |
Formula
This tool uses the standard atmosphere (troposphere) approximation with lapse rate L.
- Pressure from altitude:
P = P0 × (1 − (L × h) / T0)^(g0/(R×L)) - Altitude from pressure:
h = (T0/L) × (1 − (P/P0)^(R×L/g0))
Where P0 is sea level pressure, h is altitude (m), T0 = 288.15 K, L = 0.0065 K/m, g0 = 9.80665 m/s², and R = 287.05 J/(kg·K).
How to Use This Calculator
- Select the conversion mode.
- Enter the known value (pressure or altitude) and choose its unit.
- Set
P0(sea level pressure). Keep the default if you want standard conditions. - Click Convert to view results above the form.
- Use the CSV or PDF buttons to download a report.
FAQs
1) What is sea level pressure (P0)?
P0 is the reference pressure at sea level. Using a local P0 (from weather data) improves conversions because it accounts for real conditions instead of assuming the standard 1013.25 hPa.
2) Why do results differ from my phone altimeter?
Phone altimeters often apply sensor calibration and weather corrections. This calculator uses a standard atmosphere approximation, so results can differ when temperature and pressure patterns deviate from standard conditions.
3) What altitude range is supported?
The formulas are most accurate in the troposphere, roughly up to 11,000 meters. For much higher altitudes, a layered atmosphere model is needed for better accuracy.
4) Can I use inHg or mmHg?
Yes. You can input and export pressure in common units including hPa, Pa, inHg, mmHg, and psi. Internally the calculator converts values to Pascals for consistent computation.
5) Can this compute below sea level?
Yes. If pressure is higher than sea level pressure, the calculated altitude may be negative. This can represent locations below sea level when the reference P0 is set correctly.
6) Is this the same as aviation QNH/QFE?
This is a physics conversion tool. If you set P0 to a local sea level pressure, it behaves similarly to QNH-style altitude estimation. It does not apply all aviation-specific corrections.