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Sea Level Pressure Calculator

Convert a barometer reading at your elevation (station pressure) to sea-level pressure, or sea-level pressure back to station pressure, from altitude and temperature — in hPa, inHg, mmHg and kPa.

Units

Convert

Pressure reading

Station elevation

Air temperature at the station

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How it works

P₀ = P × [1 − 0.0065 h ÷ (T + 0.0065 h + 273.15)]^(−5.257) · P = P₀ × [1 − 0.0065 h ÷ (T + 0.0065 h + 273.15)]^5.257 · P = station pressure, P₀ = sea-level pressure, h = elevation (m), T = station air temperature (°C)

A barometer reads lower the higher it is, because there is less air above it — about 1 hPa less for every 8 m near sea level. To compare readings from different places on a weather map, meteorologists reduce station pressure to sea level with the hypsometric (barometric) equation, which assumes the air column below the station cools at the standard 6.5 °C/km. Normal sea-level pressure is 1,013.25 hPa (29.92 inHg); values below about 1,000 hPa usually mean a low-pressure system, above about 1,020 hPa a high.

Worked example

A barometer at 1,000 m reads 900.0 hPa with an air temperature of 15 °C. The bracket is 1 − 6.5 ÷ (15 + 6.5 + 273.15) = 0.97794, and 0.97794^(−5.257) = 1.1244, so the sea-level pressure is 900 × 1.1244 = 1,012.0 hPa (29.88 inHg) — near normal, 1.3 hPa below the standard atmosphere.

Sources: NOAA National Weather Service — Pressure (station vs sea-level pressure) · Wikipedia — Barometric formula

Frequently asked questions

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

Station pressure is what a barometer actually measures where it is. Sea-level pressure is that reading adjusted to what it would be at sea level, so places at different elevations can be compared. Weather reports and maps use sea-level pressure.

Why does my barometer read lower than the weather report?

Because you are above sea level. At 1,000 m the air pressure is about 11% lower; set the barometer’s sea-level offset or use this conversion.

What is normal sea-level pressure?

The standard atmosphere is 1,013.25 hPa, 29.92 inHg or 760 mmHg. Real readings range from about 950 hPa in deep storms to about 1,050 hPa in strong winter highs.

Is sea-level pressure the same as the altimeter setting (QNH)?

Close but not identical. QNH uses the standard atmosphere temperature profile instead of the actual temperature, so it can differ from this temperature-corrected sea-level pressure by a few hectopascals at high stations.

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This calculator is for educational purposes. Double-check important results before acting on them.