Pressure Converter
One Quantity, Seven Conventions
Pressure is force per unit area, and the SI unit — the pascal, one newton per square metre — is inconveniently tiny for most real work. Atmospheric pressure is about 101,325 of them. So every field invented something more usable: meteorology reached for millibars and inches of mercury, tyre gauges for PSI, medicine for millimetres of mercury, and industry for the bar. All seven are rigidly related to the pascal by defined constants, which is what makes this conversion exact.
The Formula
(Factors are relative to 1 pascal)
Unlike area or volume, no squaring or cubing is involved — each unit is a straight multiple of the pascal. Converting 32 PSI to bar runs as 32 × 6894.757293168361 ÷ 100000 = 2.20632233 bar.
The Factors and Where They Come From
| Unit | Code | Pascals per unit | Basis |
|---|---|---|---|
| Pascals | pa | 1 | SI: 1 N/m² |
| Kilopascals | kpa | 1000 | SI multiple |
| Bar | bar | 100000 | defined as 10&sup5; Pa |
| PSI | psi | 6894.757293168361 | 1 lbf per in² |
| Atmospheres | atm | 101325 | standard atmosphere, defined exactly |
| mmHg (Torr) | mmhg | 133.322387415 | 1 mm of mercury column |
| inHg | inhg | 3386.389 | 1 inch of mercury column |
One Atmosphere, Seven Ways
The clearest way to see how the units relate is to express the same physical pressure — sea-level standard atmosphere — in each:
| Unit | Value |
|---|---|
| Pascals | 101325 |
| Kilopascals | 101.325 |
| Bar | 1.01325 |
| PSI | 14.69594878 |
| mmHg (Torr) | 759.99989173 |
| inHg | 29.9212524 |
The mmHg figure lands at 759.99989 rather than a clean 760 because the modern Torr and the mmHg are defined from slightly different bases; the converter uses the conventional millimetre-of-mercury value of 133.322387415 Pa.
Full Cross-Reference
| 1 of… | Pascals | Kilopascals | Bar | PSI | Atmospheres |
|---|---|---|---|---|---|
| Pascal | 1 | 0.001 | 0.00001 | 0.00014504 | 0.00000987 |
| Kilopascal | 1000 | 1 | 0.01 | 0.14503774 | 0.00986923 |
| Bar | 100000 | 100 | 1 | 14.50377377 | 0.98692327 |
| PSI | 6894.75729317 | 6.89475729 | 0.06894757 | 1 | 0.06804596 |
| Atmosphere | 101325 | 101.325 | 1.01325 | 14.69594878 | 1 |
| mmHg (Torr) | 133.32238742 | 0.13332239 | 0.00133322 | 0.01933678 | 0.00131579 |
| inHg | 3386.389 | 3.386389 | 0.03386389 | 0.4911542 | 0.03342106 |
Tyre Pressures
Vehicle placards quote PSI in some markets and bar or kPa in others. The same reading, three ways:
| PSI | Kilopascals | Bar |
|---|---|---|
| 30 | 206.8427188 | 2.06842719 |
| 32 | 220.63223338 | 2.20632233 |
| 35 | 241.31650526 | 2.41316505 |
| 100 | 689.47572932 | 6.89475729 |
Fields That Need This
- Automotive — a tyre placard in bar against a gauge reading in PSI, or a European service manual specifying kPa.
- Meteorology and aviation — altimeter settings are given in inHg in North America and in hectopascals (equal to millibars) almost everywhere else.
- Medicine — blood pressure and vacuum levels are conventionally mmHg, while equipment specs may be in kPa.
- Process and hydraulics — system ratings in bar against instrumentation calibrated in PSI.
- Vacuum work — Torr, millibar and pascal all appear in the same datasheets.
How to Use This Calculator
- Enter the pressure reading into the Value field.
- Pick the unit it's currently in from the first dropdown.
- Pick the unit you need from the second dropdown.
- Press Calculate. The result comes with both pascal factors and the arithmetic used.
Related Calculations
Pressure is force over area — convert the area side with the Area Converter. For thermodynamic problems pairing pressure with temperature, see the Temperature Converter.