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Pressure Converter
Convert a pressure between SI, tyre, weather, medical and engineering units. Pick the unit you have and the unit you want, and the equivalent in all other units is listed beneath.
How the pressure units are defined
Pressure is force per unit area. The SI unit is the pascal, one newton per square metre. Larger units are defined from it:
- 1 bar = 100,000 Pa exactly, and 1 millibar = 1 hectopascal = 100 Pa
- 1 standard atmosphere = 101,325 Pa exactly
- 1 torr = 1/760 of a standard atmosphere ≈ 133.322 Pa
- 1 psi = one pound-force per square inch ≈ 6,894.757 Pa
- 1 technical atmosphere = 1 kgf/cm² = 98,066.5 Pa exactly
- 1 conventional mmHg = 133.322387415 Pa
Torr and conventional mmHg differ by only about one part in seven million, so for clinical and everyday work they are treated as the same.
Gauge versus absolute pressure
Many readings are measured relative to the surrounding air. A tyre gauge showing 32 psi reports gauge pressure, the excess over the atmosphere. Absolute pressure adds the ambient atmosphere, about 14.7 psi or 101.3 kPa at sea level, so a tyre at 32 psi gauge holds about 46.7 psi absolute. The converter changes only the unit, not the reference, so convert gauge to gauge and absolute to absolute.
Labels such as psig (gauge) and psia (absolute) make the difference explicit. Vacuum and some weather and scientific readings are normally absolute.
Where each unit appears
| Unit | Typical use |
|---|---|
| kPa, bar, psi | Tyres, compressed air, hydraulics and plumbing |
| hPa or mbar | Weather forecasts and barometers |
| mmHg | Blood pressure readings |
| atm | Chemistry, diving and gas laws |
| MPa | Material strength and high-pressure equipment |
Standard sea-level air pressure is 1,013.25 hPa, which is 760 mmHg or about 14.696 psi.
Mistakes and quick checks
- Confusing bar with atm. They are close but not equal: 1 bar is about 0.98692 atm, and 1 atm is 1.01325 bar.
- Ignoring the manufacturer limit. Use the converted value for convenience, but never exceed the rating printed on a tyre, cylinder or vessel.
- Dropping prefixes. 1 MPa is 1,000 kPa and 10 bar, which is easy to miss when reading specifications.
As a rule of thumb, 1 bar is about 14.5 psi and 100 kPa. A tyre quoted at 2.2 bar is therefore close to 32 psi.
Blood pressure deserves a special note. Readings in mmHg are conventionally reported in whole numbers, such as 120 over 80, and a converted kPa value (about 16.0 over 10.7) is used only where local practice requires it. This page is for unit conversion and does not interpret medical readings.
In weather work, a sea-level pressure near 1,013 hPa is regarded as average, with lower values associated with unsettled weather. Barometer readings in inches of mercury can be converted by first expressing them in mmHg, since one inch is 25.4 mm.
Worked example
A car tyre is inflated to 32 psi. What is that in bar?
Inputs
| Value | 32 |
|---|---|
| From | Pounds per square inch (psi) |
| To | Bar (bar) |
Result
32 psi = 2.206322 bar
| Pascals (Pa) | 220,632.2334 |
|---|---|
| Kilopascals (kPa) | 220.632233 |
| Megapascals (MPa) | 0.2206322 |
| Millibar (hectopascal) (mbar) | 2,206.3223 |
| Standard atmospheres (atm) | 2.177471 |
| Torr (Torr) | 1,654.8778 |
| Millimetres of mercury (mmHg) | 1,654.8776 |
| Technical atmosphere (kgf/cm²) (at) | 2.249823 |
- Factors are exact definitions where one exists; results are shown to about six significant digits.
Accuracy note: Factors use the standard definitions stated on this page. Results are rounded for display; for engineering or legal work use the full-precision factors.
Frequently asked questions
How many psi are in one bar?
One bar is about 14.5038 psi. The exact value comes from 100,000 Pa divided by 6,894.757293168 Pa per psi.
How many kilopascals are in one atmosphere?
A standard atmosphere is exactly 101.325 kilopascals, or 1,013.25 hectopascals, the usual reference for sea-level air pressure.
What is the difference between torr and mmHg?
They are almost identical. One torr is 1/760 of an atmosphere, while a conventional millimetre of mercury is 133.322387415 pascals, a relative difference of about one part in seven million.
Is millibar the same as hectopascal?
Yes. One millibar equals one hectopascal, which is 100 pascals. Weather services use either name.
Does the calculator handle gauge pressure?
It converts the unit only. Gauge and absolute readings differ by the atmosphere, so convert like with like and add or subtract the atmosphere yourself if needed.
Related calculators
More conversion references
For pressure conversion tables beyond this tool, see PakMath pressure conversion tables. PakMath is a sister project of Adzita.