Pressure Converter
Convert a pressure into psi, bar, kPa, MPa, hPa, Pa, atmospheres, torr, mmHg and kgf/cm² at once.
Pressure units and their definitions
The size of each unit in pascals is listed below. The converter first turns your pressure into pascals, then divides by the size of each unit.
| Unit | Size of one unit | Definition and source |
|---|---|---|
| Pascal (SI) | ||
| MPa (megapascal) | 1,000,000 Pa | 1,000,000 Pa (SI prefix mega) |
| kPa (kilopascal) | 1,000 Pa | 1,000 Pa (SI prefix kilo) |
| hPa (hectopascal) | 100 Pa | 100 Pa (SI prefix hecto). Equal to 1 millibar (mbar) |
| Pa (pascal) | 1 Pa | The SI unit of pressure: one newton per square meter |
| Bar and atmosphere | ||
| bar | 100,000 Pa | Exactly 100,000 Pa. NIST SP 811, Appendix B.9 |
| atm (standard atmosphere) | 101,325 Pa | Exactly 101,325 Pa. NIST SP 811, Appendix B.9 |
| Pound-force per square inch | ||
| psi (pound-force per square inch) | 8896443230521/1290320000 Pa (about 6,894.757 Pa) | About 6,894.757293 Pa, worked out from the pound (0.45359237 kg), standard gravity (9.80665 m/s²) and the inch (0.0254 m). NIST lists 6.894 757 E+03 Pa, rounded to 7 digits. NIST SP 811, Appendix B.9 |
| Millimeter of mercury and torr | ||
| mmHg (millimeter of mercury) | 20265/152 Pa (about 133.3224 Pa) | This tool uses 101,325/760 Pa (about 133.3224 Pa), the same value it uses for the torr. NIST lists the conventional mmHg as about 133.322 Pa and does not state that it equals the torr. See the note below the converter. NIST SP 811, Appendix B.9, NIST SP 811, Chapter 5 |
| Torr (torr) | 20265/152 Pa (about 133.3224 Pa) | Exactly 101,325/760 Pa (about 133.3224 Pa), the definition given in NIST SP 811, Chapter 5. NIST SP 811, Appendix B.9, NIST SP 811, Chapter 5 |
| Kilogram-force per square centimeter (engineering unit) | ||
| kgf/cm² (kilogram-force per square centimeter) | 98,066.5 Pa | Exactly 98,066.5 Pa (1 kgf = 9.80665 N, per square centimeter). An engineering unit that is not an SI unit. NIST SP 811, Appendix B.9 |
The calculation uses exact fractions, and the only rounding is the one applied when a value is displayed.
Absolute pressure and gauge pressure are a separate matter
- Absolute pressure is measured from a perfect vacuum (zero pressure). It is written psia, bar(a), MPaA and so on.
- Gauge pressure is measured with the surrounding atmospheric pressure as zero (absolute pressure − atmospheric pressure). It is written psig, bar(g), MPaG and so on. Tire pressure and most readings on a pressure gauge are gauge pressures.
- This tool converts units only. For example, a gauge pressure of 35 psi is a gauge pressure of about 241.3 kPa (it does not become an absolute pressure).
- Converting between gauge and absolute pressure means adding or subtracting the atmospheric pressure, which is a different calculation. The atmospheric pressure changes with place, weather and altitude (the standard atmosphere of 101,325 Pa is only a reference value), so this tool does not include that conversion.
About mmHg and the torr
- Torr: NIST SP 811 (Chapter 5) gives the torr as exactly 101,325/760 Pa (about 133.3224 Pa).
- Millimeter of mercury (mmHg): NIST SP 811 gives 1 mmHg as approximately 133.322 Pa (Chapter 5), and lists both the "conventional" millimeter of mercury and the torr at 1.333 224 E+02 Pa in Appendix B.9 (neither is marked exact), the same seven digits. The pages we read do not state that the torr and the millimeter of mercury are the same unit, and a real column of mercury gives a pressure that depends on the density of mercury (which changes with temperature) and on gravity.
- What this tool does: to keep the converter simple, it uses the same value, 101,325/760 Pa, for both the torr and the mmHg. For mmHg this is therefore an approximation of the conventional definition. The two values agree to the seven digits that NIST lists, but this tool does not claim they are exactly equal. If you need the conventional mmHg to more digits (for example in a metrological context), use the definition from the standard you are working with.
- NIST SP 811 Chapter 5 lists the millimeter of mercury among the units accepted for use with the SI (while discouraging its use by NIST authors) and puts the torr in its list of unacceptable units. The torr and the mmHg are still widely used in medicine (blood pressure) and vacuum technology.
About psi
1 psi (pound-force per square inch) is converted with a value of about 6,894.757293 Pa, worked out from the pound (0.45359237 kg), standard gravity (9.80665 m/s²) and the inch (0.0254 m). NIST lists the factor as 6.894 757 E+03 Pa, rounded to seven digits, which agrees.
About kgf/cm²
The kilogram-force per square centimeter (kgf/cm²) is an engineering unit that is not part of the SI. This tool converts it with 1 kgf/cm² = 98,066.5 Pa (1 kgf = 9.80665 N). It is still seen in older gauges and equipment specifications. It also equals the "technical atmosphere".
Examples
- 1 atm = 101,325 Pa = 101.325 kPa = 1.01325 bar = 760 mmHg = about 14.69595 psi
- 1 bar = 100,000 Pa = about 14.50377 psi
- 35 psi = about 241.3165 kPa = about 2.413165 bar
- 1 MPa = about 10.19716 kgf/cm²
- 120 mmHg = about 15.99868 kPa (the upper number of a blood pressure reading, as an example)
- 1 hPa = 100 Pa = 1 mbar (the unit of pressure in weather forecasts)
Notes
- You can enter decimals (up to 12 digits before the decimal point and 6 decimal places). Thousands separators such as 1,234.5 are accepted; use a period as the decimal separator. Negative pressures cannot be entered (an absolute pressure is 0 or more).
- For anything involving the design or safety of equipment, check the pressure and the unit in the specification or the standard for that equipment.
- To convert other units, use the Area Converter, the Volume Converter or the Weight & Mass Converter.
Sources
The definitions on this page come from the sources below (checked on November 1, 2026). Some values are exact by definition, and a source may list them rounded; the notes in the table say how each value is defined. The pressure rows of Appendix B.9 were read word for word on November 1, 2026. The text of footnotes [8] and [12] that the table refers to (for example, for the conventional millimeter of mercury) was not read.
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science (pressure or stress)
- NIST Guide to the SI, Chapter 5: Units Outside the SI
Frequently asked questions
How many pascals are in one atmosphere?
101,325 Pa (about 1013.25 hPa, about 1.01325 bar). This is the standard atmosphere.
How many kPa are in one bar?
100 kPa (100,000 Pa). A pressure of 1 bar is about 1.3% smaller than 1 atm.
How many kPa is a tire pressure of 2.5 kgf/cm²?
About 245.2 kPa (1 kgf/cm² = 98.0665 kPa). A tire pressure reading is a gauge pressure.
Are mmHg and torr the same?
Not by definition. The torr is exactly 101,325/760 Pa. The conventional millimeter of mercury is listed at about 133.322 Pa. This converter uses 101,325/760 Pa for both, so for mmHg it is an approximation.