Sea level pressure calculator
This sea level pressure calculator turns the pressure measured at your location into a sea level value (altimeter setting): a barometer at 2,000 ft reading 27.85 inHg corresponds to about 29.94 inHg at sea level. Enter station pressure and elevation – or an altimeter setting to get the pressure at your elevation.
How it is calculated
Altimeter setting = (P − 0.3) × (1 + 0.0065 × 1013.25^0.190284 ÷ 288 × h ÷ (P − 0.3)^0.190284)^(1 ÷ 0.190284), with P = station pressure in millibars (hPa) and h = elevation in meters. This is the National Weather Service (NWS) formula; it rests on the standard atmosphere with 1013.25 mb and a temperature drop of 0.0065 °C per meter. In the other direction the NWS gives station pressure = altimeter setting × ((288 − 0.0065 × h) ÷ 288)^5.2561. The 0.3 mb is part of the NWS equation, which is why the round trip at standard pressure up to 3,000 m ends 0.3 to 0.5 mb lower.
Station pressure for 29.92 inHg at sea level
| Elevation | Station pressure |
|---|---|
| 0 ft | 29.92 inHg |
| 500 ft | 29.38 inHg |
| 1,000 ft | 28.85 inHg |
| 2,000 ft | 27.82 inHg |
| 3,000 ft | 26.81 inHg |
| 5,000 ft | 24.89 inHg |
Near the ground the pressure drops by roughly 1 inHg per 1,000 ft in this table. Example: a barometer at 2,000 ft reads 27.85 inHg; reduced to sea level that is 29.94 inHg, or 1014 hPa.
Why reduce to sea level?
Weather maps and reports give pressure at sea level so that highs and lows can be compared no matter how high a station sits. The World Meteorological Organization (WMO) asks for this reduction at all stations where it can be done with reasonable accuracy. The altimeter setting (QNH) uses the standard atmosphere instead of the actual temperature, and the WMO notes that it therefore differs from the sea level pressure in weather reports. It also notes that several methods are in use – a recommended standard equation, the “international formula” and simplified methods – so your weather service’s figures may differ a little from this calculator.
Standard pressure in other units
Standard sea level pressure of 1013.25 hPa equals 760 mmHg and 29.92 inHg (NIST: 1 inHg = 33.863 89 hPa, 1 mmHg = 1.333 224 hPa); 1 hPa is exactly 1 mb. For bar and psi use the pressure converter; pilots who need density altitude can continue with the density altitude calculator.
Frequently asked questions
What is normal sea level pressure?
Standard pressure is 1013.25 hPa, which is 29.92 inHg or 760 mmHg. Actual readings change with the weather – higher in a high-pressure system, lower in a low.
How do I convert station pressure to sea level pressure?
Put the station pressure and your elevation into the NWS altimeter setting formula. 27.85 inHg at 2,000 ft gives 29.94 inHg at sea level.
Is altimeter setting the same as sea level pressure?
Not quite. The altimeter setting (QNH) is reduced to sea level with the standard atmosphere and is used to set aircraft altimeters. Sea level pressure in weather reports is reduced with the actual temperature, and the WMO notes that QNH differs from it.
What is the sea level pressure formula without temperature?
The NWS formula above needs only station pressure and elevation. It assumes the standard atmosphere, so no temperature is entered.
How should I set my home weather station?
If your station asks for elevation or an offset, the table in the result shows the difference between station pressure and sea level pressure that you can use as that offset.
Sources and legal basis
- National Weather Service (El Paso), Wxcalc “Altimeter Setting”: A = (P − 0,3) × (1 + (1013,25^0,190284 × 0,0065 ÷ 288) × h ÷ (P − 0,3)^0,190284)^(1/0,190284), P in mb, h in m (read 10.10.2026)
- National Weather Service (El Paso), Wxcalc “Station Pressure”: P_stn = A × ((288 − 0,0065 × h) ÷ 288)^5,2561 (read 10.10.2026)
- WMO-No. 8 (2008), Guide to Meteorological Instruments and Methods of Observation: Part I, 3.11 (reduction to mean sea level), Part II, 1.3.2.6 (standard equation, “international formula” and simplified methods in use), Part II, 2.9.1 (p. II.2–12: QNH uses the ICAO standard atmosphere “and not the current true state of the atmosphere”, so it differs from sea-level pressure reduced with the actual temperature) (read 10.10.2026)
- NIST SP 811, Appendix B.8: inHg = 3,386 389 kPa, mmHg = 133,3224 Pa, mbar = 100 Pa, ft = 0,3048 m (read 10.10.2026)
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