What is the difference between station pressure and sea level pressure?

Station pressure is the actual atmospheric pressure at the altitude of the measuring instrument. Sea level pressure (MSLP) is what the pressure would be if the station were at sea level. Because air pressure decreases with altitude, a high-elevation station always reads lower than its MSLP equivalent.

Can MSLP be used as an aircraft altimeter setting (QNH)?

No. MSLP accounts for actual ambient temperature and standard lapse rate to model the real atmosphere for synoptic meteorology. Aviation altimeter settings (QNH) assume the International Standard Atmosphere (ISA) without temperature corrections. Setting an altimeter to MSLP during non-standard temperatures can produce dangerous altitude errors. Always obtain official QNH from ATIS, AWOS, or ATC for flight operations.

Which formula does this calculator use?

The calculator uses the standard WMO barometric reduction formula: MSLP = P × exp(g × H / (R × Tv)), where P is station pressure, g is gravitational acceleration (9.80665 m/s²), H is station elevation, R is the specific gas constant for dry air (287.05 J/(kg·K)), and Tv is the virtual temperature estimated from the measured temperature.

Why does temperature matter?

Temperature affects air density. Warmer air is less dense, so the same pressure difference corresponds to a greater height difference. Including the actual station temperature makes the reduction more accurate than using a fixed standard atmosphere temperature.

How accurate is this calculator?

For most surface weather purposes the result is accurate to within 0.1–0.5 hPa. Accuracy decreases slightly at very high elevations (>2000 m) where the linear temperature approximation deviates more from the real atmosphere.

What units does the calculator accept?

Elevation: meters or feet. Pressure: hPa/mb or inHg. Temperature: °C or °F. All conversions are handled automatically before the calculation.

Sea Level Pressure Reduction Calculator

Convert station (observed) pressure to mean sea level pressure (MSLP) using elevation and temperature.

Station Parameters

Station Elevation

Observed Station Pressure

Station Air Temperature

Aviation safety notice: MSLP accounts for actual ambient temperature for meteorological mapping and differs from aviation altimeter settings (QNH/QNE), which assume a standard atmosphere. Never dial MSLP into an aircraft altimeter.

Result

Enter values and click Calculate.

Quick Reference — Typical MSLP Ranges

Condition	MSLP (hPa)	MSLP (inHg)
Standard atmosphere	1013.25	29.92
Strong high (anticyclone)	> 1030	> 30.42
Fair weather	1013 – 1030	29.92 – 30.42
Unsettled / low approach	995 – 1013	29.38 – 29.92
Deep low / storm	< 980	< 28.94

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Summary

Convert station (observed) pressure to mean sea level pressure (MSLP) using elevation and temperature.

How it works

Enter your station elevation in meters or feet.
Enter the observed (station) pressure in hPa, mb, or inHg.
Enter the current air temperature at the station in °C or °F.
Click Calculate to apply the standard barometric reduction formula.
The result shows MSLP in hPa/mb and inHg, along with the pressure difference.

Use cases

Normalize home weather station readings to compare with official forecasts.
Compare surface observations against regional synoptic weather charts.
Study synoptic pressure patterns across terrain at different elevations.
Convert raw sensor data from high-altitude IoT weather nodes.
Cross-check readings from personal barometers against METAR reports.
Classroom demonstrations of the standard atmosphere.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu