Pressure Converter
Convert between pascals, hectopascals, bars, millibars, psi, atmospheres, torr and millimetres of mercury.
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1 bar
14.50377 psi
Pound per square inch
In every unit
| Unit | Symbol | Value |
|---|---|---|
| Pascal | Pa | 100,000 |
| Hectopascal | hPa | 1,000 |
| Kilopascal | kPa | 100 |
| Megapascal | MPa | 0.1 |
| Bar | bar | 1 |
| Millibar | mbar | 1,000 |
| Standard atmosphere | atm | 0.9869233 |
| Pound per square inch | psi | 14.50377 |
| Torr | Torr | 750.0617 |
| Millimetre of mercury | mmHg | 750.0616 |
Tyre pressure is in bar or psi, weather forecasts are in hectopascals, blood pressure is in millimetres of mercury, and the SI unit behind all of them is the pascal.
How it works
Every unit is expressed in pascals and conversions go through it. A pascal is one newton per square metre, which is a very small pressure — hence the hectopascal on weather maps and the bar, defined as exactly 100 000 pascals, on a tyre gauge.
The standard atmosphere is defined as exactly 101 325 pascals. A hectopascal and a millibar are the same size, which is why a forecast reading 1013 hPa and one reading 1013 mbar say the same thing.
Examples
| Case | Input | Result |
|---|---|---|
| A bar in psi | 1 bar | 14.50377 psi |
| Standard atmosphere, as a barometer reads it | 1 atm | 1,013.25 hPa |
| A tyre pressure | 2.3 bar | 33.35868 psi |
Frequently asked questions
Why are the torr and the millimetre of mercury both listed?
Because they are defined separately and are very nearly, but not exactly, equal. A torr is one 760th of a standard atmosphere. A millimetre of mercury is the pressure of a one millimetre column at a defined density and gravity. They differ by about one part in seven million — invisible for a blood pressure reading, and not something to merge in a converter.
Is tyre pressure absolute or relative?
A tyre gauge reads gauge pressure, which is the amount above the surrounding air. This page converts the number, whatever it means: 2.5 bar on a gauge converts to 36.26 psi on a gauge. Converting to absolute pressure means adding an atmosphere first, and that is a decision about your reading rather than about the units.
Good to know
- Every factor used here is an exact definition rather than a rounded measurement, so the only error in a result is the one that comes from displaying it with a finite number of digits.