Barometric Pressure Converter
Convert barometric pressure between inHg, hPa, mbar, mmHg, atm, and psi.
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Barometric (atmospheric) pressure is measured in several units.
Standard atmospheric pressure at sea level:
- 29.92 inHg (inches of mercury)
- 1013.25 hPa (hectopascals)
- 1013.25 mbar (millibars) — same as hPa
- 760 mmHg (millimeters of mercury)
- 1 atm (atmosphere)
- 14.696 psi (pounds per square inch)
Conversion factors (from 1 inHg):
- 1 inHg = 33.8639 hPa = 33.8639 mbar
- 1 inHg = 25.4 mmHg
- 1 inHg = 0.49115 psi
Weather context:
- High pressure (fair weather): 30.20+ inHg (1023+ hPa)
- Normal pressure: 29.80-30.20 inHg (1009-1023 hPa)
- Low pressure (storms): < 29.80 inHg (< 1009 hPa)
- Hurricane central pressure: < 28.00 inHg (< 948 hPa)
What forecasters actually watch is the trend, not the snapshot. Falling pressure usually means an approaching low and unsettled or stormy weather; steadily rising pressure points to clearing skies and calm. That’s why old barometers were marked “Stormy,” “Change,” and “Fair” rather than with numbers, and why the direction of movement tells you more than any single reading.
One subtlety behind the figures: the pressure in a weather report is corrected to sea level, not the raw reading at the station. Without that correction a mountain town would always look alarmingly low simply because there’s less atmosphere above it, and no two places could be compared. So the “1013 hPa” on a forecast is a standardized, sea-level-equivalent value, which is what makes a national pressure map meaningful at a glance.
How we build and check this converter
This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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