Weather reports give air pressure in inches of mercury in the U.S., hectopascals or millibars almost everywhere else, and millimetres of mercury in some countries. Standard sea-level pressure is 29.92 inHg = 1013.25 hPa.
How to use the Barometric Pressure Converter
- Pick the unit you are starting from in the From menu and type your value.
- Pick the unit you want in the To menu. The heading changes to match – for example “Inches of Mercury to Hectopascals Converter”.
- The most common pressure units are shown below at the same time, so you can compare them at a glance.
- Type into any result to convert backwards, then use Copy results – the copied text starts with the heading for your chosen units.
Results update as you type. Everything is calculated in your browser.
How it works
Every pressure unit is defined by an exact factor relative to the pascal (the base unit). The calculator first turns the value you type into pascals, then turns that into the unit you picked in the “To” menu and into each of the common units below it. This two-step method means any unit can be converted to any other – 18 units are available in each menu – and you can type into any field, including a result, to work in the other direction. Changing a unit menu keeps the quantity the same and just re-expresses it, and the page heading and copied results follow your choice.
How to convert pressure units
- Choose the unit you have in the From menu and type the value, for example 29.92 inHg.
- Choose the unit you want in the To menu, for example hectopascals. The page heading changes to “Inches of Mercury to Hectopascals Converter”.
- The calculator multiplies by the pascal factor of the “from” unit and divides by the factor of the “to” unit: 29.92 inHg × 3,386.389 ÷ 100 = 1,013.2076 hPa.
1 inch of mercury in common units
| Unit | Value |
|---|---|
| Hectopascals (hPa) | 33.86389 |
| Millibars (mbar) | 33.86389 |
| Millimetres of mercury (mmHg) | 25.400003 |
| Kilopascals (kPa) | 3.386389 |
| Standard atmospheres (atm) | 0.033421061 |
| Psi (psi) | 0.4911542 |
Inches of mercury conversion table
| Inches of mercury | hPa | mbar | mmHg | kPa |
|---|---|---|---|---|
| 28.5 | 965.12087 | 965.12087 | 723.90008 | 96.512087 |
| 29 | 982.05281 | 982.05281 | 736.60008 | 98.205281 |
| 29.5 | 998.98475 | 998.98475 | 749.30008 | 99.898476 |
| 29.92 | 1,013.2076 | 1,013.2076 | 759.96808 | 101.32076 |
| 30.2 | 1,022.6895 | 1,022.6895 | 767.08008 | 102.26895 |
| 30.5 | 1,032.8486 | 1,032.8486 | 774.70008 | 103.28486 |
What is an inch of mercury?
Inches of mercury are used for barometric pressure in U.S. weather reports and aviation altimeter settings; standard pressure is 29.92 inHg.
Common mistakes to avoid
Mixing gauge pressure (psig, barg) with absolute pressure (psia, bara), treating bar and atm as identical, and confusing kgf/cm² with bar.
Formula
1 inHg = 33.86389 hPa1 inHg = 33.86389 mbar1 inHg = 25.400003 mmHg1 inHg = 3.386389 kPa1 inHg = 0.033421061 atmWorked example
Inputs — From: 29.92 inHg.
Results — To = 1,013.2075888 hPa; Millibars = 1,013.2075888 mbar; Millimetres of mercury = 759.96808071 mmHg; Kilopascals = 101.32075888 kPa; Standard atmospheres = 0.99995814 atm; Psi = 14.69533365 psi.
Frequently asked questions
What is normal barometric pressure?
About 29.92 inHg, 1013.25 hPa or 760 mmHg at sea level.
What counts as low pressure?
Below about 1000 hPa (29.53 inHg) usually means unsettled weather.
Are hPa and mbar the same?
Yes, 1 hPa = 1 mbar.
How do I change the units?
Pick any unit in the From and To menus. The value is converted in place, and the heading changes to show your conversion, for example “Inches of Mercury to Hectopascals Converter”.
Can I type into any field?
Yes. Every field is editable, so you can start from whichever unit you have.
How many units can I convert between?
18 pressure units, from the everyday to the specialised.
Which units are exact?
All factors here are exact by definition except astronomical and similar reference values, which use internationally agreed constants.
What formula does the Barometric Pressure Converter use?
1 inHg = 33.86389 hPa.