Station to Sea Level Pressure Calculator
Atmospheric pressure falls with height, so a barometer reading depends on the station's elevation. To compare pressures between places, and to draw the isobars on a weather map, readings are reduced to a common datum: mean sea level. This tool converts station pressure to sea level pressure using the station's elevation above sea level and the air temperature, applying the standard barometric reduction. Enter the measured station pressure in hectopascals, the elevation in metres, and the temperature in degrees Celsius. The result is the equivalent sea level pressure that meteorologists report and plot.
Sea level pressure reduction formula
P_sea = P_station * (1 + (0.0065 * h) / (T + 0.0065 * h + 273.15)) ^ 5.257
where h = elevation in metres and T = temperature in degrees Celsius
The reduction multiplies station pressure by a factor that grows with elevation and shrinks with temperature. The lapse rate 0.0065 degrees per metre and the exponent 5.257 come from the standard atmosphere and the properties of air. The term in the denominator converts to absolute temperature with the 273.15 offset. Taller, colder stations get a larger upward correction because the imagined air column below them would be denser.
Worked example
A station at 500 metres reads 950 hPa with an air temperature of 15 degrees Celsius. The lapse term 0.0065 * 500 = 3.25. The bracket is 1 + 3.25 / (15 + 3.25 + 273.15) = 1 + 3.25 / 291.4 = 1.01115. Raised to the power 5.257 gives 1.0590. So sea level pressure = 950 * 1.0590 = 1,007.04 hPa, a reduction of 57.04 hPa added to bring the reading to the sea level datum.
Frequently asked questions
Why reduce station pressure to sea level?
Because pressure changes strongly with elevation, raw readings from stations at different heights are not directly comparable. Reducing each to mean sea level removes the elevation effect, leaving only the weather-driven pressure pattern. This is what lets meteorologists draw isobars and identify highs and lows on a synoptic chart.
What temperature should I enter?
Use the current air temperature at the station. Official reductions often use a temperature averaged over the previous twelve hours to smooth out daily swings, but the instantaneous temperature gives a good approximation for most purposes. The temperature is a user-editable input so you can apply whichever convention you need.
How is this different from altimeter setting?
Both reduce station pressure to a reference, but the aviation altimeter setting (QNH) uses the standard-atmosphere temperature profile rather than the actual temperature, so an altimeter set to it reads field elevation on the ground. The meteorological sea level pressure here uses actual temperature and is intended for weather analysis, not altimetry.
Does the formula work for very high stations?
The reduction becomes increasingly uncertain at high elevations because it depends on assumptions about the fictitious air column below the station, which does not really exist. For mountain stations above roughly 1,000 metres, national weather services apply more elaborate reduction methods. Treat results for very high stations as approximate.
Official sources
- NOAA National Weather Service: pressure reduction and analysis.
- World Meteorological Organization: Guide to Instruments and Methods of Observation.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.