Barometric Pressure Calculator
Why Weather Reports Always Adjust for Altitude
Air pressure drops predictably as you go up in elevation, simply because there's less atmosphere pressing down from above. That creates a problem for weather reporting: a mountain station and a coastal station will always read different pressures even under identical weather conditions, purely because of elevation. Meteorologists solve this by converting every station's raw reading to its sea-level equivalent, which is what actually appears on weather maps and forecasts.
The Formulas
Station-to-sea-level: P0 = Pstation ÷ (1 − (0.0065×h)/T0)5.255
P0 is sea-level pressure in hPa, h is altitude in meters, and T0 is temperature in Kelvin (standard atmosphere assumes 288.15 K, or 15°C). This is the standard barometric formula derived from the International Standard Atmosphere model, and it's the same relationship used to convert a raw station reading into the "altimeter setting" pilots and meteorologists rely on.
Worked Examples
| Altitude | Pressure at altitude |
|---|---|
| 500 m | 954.62 hPa |
| 1,500 m | 845.59 hPa |
| 3,000 m | 701.13 hPa |
Pressure falls roughly 12% per 1,000 meters near sea level, though the relationship is not perfectly linear and flattens somewhat at higher altitudes.
Where This Matters
- Reading weather maps correctly — every isobar and pressure system on a forecast map uses sea-level-adjusted values, so raw station pressure at a mountain location would otherwise appear anomalously low.
- Aviation altimeter settings — pilots use a sea-level-equivalent pressure (QNH) to calibrate altimeters so aircraft at different airports read consistent altitude.
- Home weather stations — a personal weather station at elevation needs this correction applied, or its readings won't match official regional forecasts.
How to Use This Calculator
- Choose a mode: Sea-Level Pressure → Pressure at Altitude, or Station Pressure → Sea-Level Equivalent.
- For the first mode: enter Sea-Level Pressure in hPa (defaults to 1013.25), Altitude in meters, and Temperature in Kelvin (defaults to 288.15).
- For the second mode: enter Station Pressure in hPa, Altitude in meters, and Temperature in Kelvin.
- Select Calculate to see the converted pressure.
Related Calculations
Check whether pressure trends align with storm development using the Storm Surge Calculator, or review air quality conditions with the Air Quality Index Calculator.