Guide
Normal barometric pressure, and how to convert hPa, inHg and kPa
Short answer
Standard sea-level pressure is 1013.25 hPa, which is the same as 1013.25 millibars, 29.92 inches of mercury and 101.325 kPa. Readings above that are higher than average and usually go with settled weather; readings below are lower than average and often go with unsettled weather. The records show how far it can stretch: 870 hPa in the eye of Typhoon Tip in 1979 and 1083.8 hPa in Siberia in 1968. To convert, multiply inHg by 33.86 to get hPa, divide hPa by 10 to get kPa, and remember that 1 hPa is exactly 1 mb. A barometer at altitude reads lower than the sea-level figure in weather reports, and that is normal.
What “normal” means
Meteorologists use a standard atmosphere as a reference: at sea level, 1013.25 hPa, or 29.92 inHg, as NOAA puts it. It is an average, not a target. Pressure at any place drifts above and below it as high- and low-pressure systems pass, and a reading of 1005 or 1022 hPa is perfectly ordinary weather.
So “normal” is less useful than two other questions: is the pressure higher or lower than usual where you are, and which way is it moving? A reading 10 hPa below standard that has been steady for two days tells you less about the coming hours than a reading that has dropped 6 hPa since breakfast.
hPa, mb, inHg and kPa explained
- Hectopascal (hPa). The SI unit used by the UK Met Office and in the studies quoted throughout this site. One hectopascal is 100 pascals.
- Millibar (mb or mbar). Exactly the same size as a hectopascal, as the Met Office notes: 1 hPa = 1 mb. Older charts and American forecasters often say millibars.
- Inches of mercury (inHg). Together with millibars, one of the two most common units in the United States, according to NOAA. It dates from mercury barometers, where air pressure held up a column of mercury about 30 inches tall.
- Kilopascal (kPa). Ten hectopascals. Some weather services publish pressure in kPa, which makes standard pressure 101.3.
- Millimetres of mercury (mmHg). Still seen on some older barometers; standard pressure is 760 mmHg.
Conversion table
| hPa (mb) | inHg | kPa | mmHg |
|---|---|---|---|
| 960 | 28.35 | 96.0 | 720.1 |
| 970 | 28.64 | 97.0 | 727.6 |
| 980 | 28.94 | 98.0 | 735.1 |
| 990 | 29.23 | 99.0 | 742.6 |
| 1000 | 29.53 | 100.0 | 750.1 |
| 1005 | 29.68 | 100.5 | 753.8 |
| 1010 | 29.83 | 101.0 | 757.6 |
| 1013.25 (standard) | 29.92 | 101.3 | 760.0 |
| 1015 | 29.97 | 101.5 | 761.3 |
| 1020 | 30.12 | 102.0 | 765.1 |
| 1025 | 30.27 | 102.5 | 768.8 |
| 1030 | 30.42 | 103.0 | 772.6 |
| 1040 | 30.71 | 104.0 | 780.1 |
| 1050 | 31.01 | 105.0 | 787.6 |
The formulas: inHg = hPa ÷ 33.8639; kPa = hPa ÷ 10; mmHg = hPa ÷ 1.33322.
Converting a change, not just a reading
Studies and alerts talk about changes, and small numbers in inHg are easy to misjudge. A few useful equivalents:
| Change in hPa | inHg | kPa | Where you will meet it |
|---|---|---|---|
| 1 | 0.03 | 0.1 | The smallest step most forecasts show |
| 3 | 0.09 | 0.3 | A Met Office “rising” or “falling” tendency over three hours (1.6–3.5 hPa) |
| 6 | 0.18 | 0.6 | A major change in Barometric Pressure Tracker when it happens within six hours |
| 10 | 0.30 | 1.0 | The upper end of the 6–10 hPa range in a Japanese migraine study |
| 24 | 0.71 | 2.4 | NOAA's 24-hour threshold for a rapidly deepening storm at 60° latitude |
Why your barometer reads lower than the forecast
Air pressure falls with height, by roughly 1 hPa for every 8 metres near sea level. A barometer, including the one in many phones, measures the pressure where it is: station pressure. Weather services convert station readings to sea level so that maps compare like with like, and that sea-level figure is what forecasts, this site's pressure chart and the app show.
| Height | Station pressure |
|---|---|
| 100 m (330 ft) | about 1001 hPa |
| 300 m (980 ft) | about 978 hPa |
| 500 m (1,640 ft) | about 955 hPa |
| 1,000 m (3,280 ft) | about 899 hPa |
| 1,609 m (5,280 ft, Denver) | about 834 hPa |
If you live in the hills and your phone shows 950 hPa, nothing is wrong. For spotting changes, either number works, as long as you compare like with like.
High pressure, low pressure and the extremes
High-pressure systems tend to bring settled, often clear weather; lows bring cloud, wind and rain more often, and a falling barometer is the classic sign that one is approaching. Neither is a rule: a high can trap fog for days, and a weak low can pass with barely a shower.
The World Meteorological Organization's archive of extremes puts the range in perspective. The lowest sea-level pressure on record is 870 hPa, in the eye of Typhoon Tip over the western Pacific on 12 October 1979. The highest at a station below 750 m is 1083.8 hPa at Agata in Siberia on 31 December 1968. Everyday weather in most places stays far from both.
The speed of change matters more than the level. NOAA calls a storm “bombogenesis” when the pressure at its centre falls at least 24 hPa in 24 hours at 60° latitude, or about 17.8 hPa at the latitude of New York.