Sea Level Pressure Adjustment Calculator
A barometer reads lower the higher it sits, so raw station pressure cannot be compared between places at different elevations. Reducing each reading to mean sea level strips out the height effect, which is what lets a weather map show coherent highs and lows. The hypsometric reduction scales the station pressure up by a factor that depends on the elevation and the air temperature. Enter your station pressure, elevation, and temperature, and this calculator returns the equivalent sea level pressure in hectopascals and inches of mercury.
Pressure reduction formula
factor = (1 + (0.0065 x h) / (T + 0.0065 x h + 273.15))^5.257
Sea level pressure = station pressure x factor
inHg = hPa x 0.0295300
Correction = sea level pressure - station pressure
h is station elevation in meters and T is the station temperature in degrees Celsius. The exponent 5.257 follows from the standard atmosphere temperature lapse rate of 0.0065 K per meter.
Pressure notes
- Near sea level, pressure falls about 1 hPa per 8 meters of height.
- The reduction uses the actual station temperature, not a fixed standard value.
- 1 hectopascal equals 1 millibar; 1 inch of mercury equals about 33.864 hPa.
- Sea level pressures let stations at different heights be compared on one map.
- For exact agency products, use the official station reduction constants for your site.
Sea level pressure: frequently asked questions
Why adjust station pressure to sea level?
Air pressure falls with height, so a barometer reading at an elevated station is always lower than it would be at sea level. To compare pressures across stations and draw meaningful weather maps, each reading is reduced to mean sea level, removing the effect of station elevation.
What is the sea level pressure formula?
A common hypsometric reduction is P0 = P x (1 + (0.0065 x h) / (T + 0.0065 x h + 273.15)) raised to the power 5.257, where P is station pressure, h is elevation in meters, and T is temperature in degrees Celsius. The exponent comes from the standard atmosphere lapse rate.
How much does pressure change with altitude?
Near sea level, pressure falls by roughly 1 hectopascal for every 8 meters of ascent. So a station 100 meters above sea level reads about 12 hectopascals lower than sea level. The exact reduction depends on temperature, which is why it is a required input.
What units does this calculator use?
Enter station pressure in hectopascals (equal to millibars), elevation in meters, and temperature in degrees Celsius. The reduced sea level pressure is returned in hectopascals and also converted to inches of mercury for North American use.
Is this the same as an altimeter setting?
It is closely related but not identical. The altimeter setting used in aviation reduces station pressure to sea level assuming a standard temperature profile, whereas this reduction uses the actual station temperature. Both aim to express pressure as if measured at sea level.
Official sources
- NOAA National Weather Service: Weather Calculators.
- NOAA National Weather Service: weather.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.