Pressure converter
Convert between pascals, bar, psi, atmospheres, mmHg and kgf/cm². Tyre, blood and weather pressure reference tables.
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Every pressure unit, one page
Pick any two units above. The conversions people look up most often have dedicated pages with reference tables, linked below.
The factors
| Unit | Pascals | Note |
|---|---|---|
| Pascal | 1 | SI — one newton per square metre |
| Kilopascal | 1000 | |
| Megapascal | 1,000,000 | |
| Bar | 100,000 | defined as exactly 100 kPa |
| Pound per square inch | 6894.757293 | exact, from the pound and the inch |
| Standard atmosphere | 101,325 | exact by definition |
| Millimetre of mercury | 133.322387415 | conventional |
| Kilogram-force per cm² | 98,066.5 | exact |
Four communities, four units
Pressure is measured in whatever the field settled on, and the fields do not talk to each other:
| Unit | Used for |
|---|---|
| psi | tyres, compressed air, plumbing — US and much of Asia |
| bar | tyres and industry in Europe; diving |
| kPa / hPa | scientific work, and weather as hectopascals |
| mmHg | blood pressure and vacuum, worldwide |
| kgf/cm² | older gauges and pressure vessel plates |
A tyre gauge sold in Taiwan is usually marked in psi and kgf/cm². The two look interchangeable and are 2% apart.
mmHg is not exactly one 760th of an atmosphere
The torr is. The millimetre of mercury is defined from mercury’s density and standard gravity, and comes out at 133.322387415 Pa, so:
760 mmHg = 101,325.014 Pa
1 atm = 101,325 PaA gap of 14 parts per million. It has no consequence for blood pressure and does have one for precision vacuum work, which is why both units still exist. This converter uses the conventional mmHg.
Absolute or gauge
Almost every practical pressure reading is a gauge pressure: how much above the surrounding air, not how much in total. A tyre inflated to 32 psi holds about 46.7 psi absolute, because the atmosphere is already pushing 14.7 psi.
Unit conversion does not change which kind you have. Converting 32 psi gauge gives 2.21 bar
gauge, never 3.22 bar absolute. Where it matters — diving, vacuum, engine work — the
notation is psig and bara or an explicit “gauge”/“absolute”.
Reference pressures
| kPa | bar | psi | mmHg | |
|---|---|---|---|---|
| Sea-level atmosphere | 101.3 | 1.013 | 14.70 | 760 |
| Car tyre | 220 | 2.20 | 31.9 | 1650 |
| Road bicycle tyre | 690 | 6.90 | 100 | — |
| Espresso machine | 900 | 9.00 | 130.5 | — |
| Blood pressure, systolic | 16.0 | 0.16 | 2.32 | 120 |
| Deep typhoon centre | 92.0 | 0.92 | 13.3 | 690 |
| 10 m under water | 202.7 | 2.03 | 29.4 | 1520 |
Every 10 metres of sea water adds almost exactly one atmosphere, which is the basis of most diving arithmetic.
Where people go wrong
Hectopascals and millibars are the same number. A forecast saying 1013 hPa and one saying 1013 mbar are identical; the unit was renamed, not rescaled.
Doubling the gauge pressure does not double the air inside. Going from 30 to 60 psi gauge takes the absolute pressure from 44.7 to 74.7 — an increase of two thirds, not double.