Pressure Unit Converter
Convert one pressure across eleven units at once (Pa, hPa, kPa, MPa, bar, atm, psi, torr, mmHg, inHg, mmH2O) with exact NIST SP 811 factors, and torr distinguished from mmHg.
One pressure, eleven scales. Type a value in any unit and this converter shows it in every other unit at once, so getting from bar to psi to atmospheres never means chaining two separate lookups. Every factor comes from NIST SP 811, and torr sits in its own row apart from millimetres of mercury, because at full precision they are two different units.
| Unit | Symbol | Value |
|---|---|---|
| pascal | Pa | - |
| hectopascal | hPa | - |
| kilopascal | kPa | - |
| megapascal | MPa | - |
| bar | bar | - |
| standard atmosphere | atm | - |
| pound-force per square inch | psi | - |
| torr | torr | - |
| millimetre of mercury | mmHg | - |
| inch of mercury | inHg | - |
| millimetre of water | mmH2O | - |
Enter a pressure to convert.
Which conventions this uses
- Standard atmosphere
- 101325 Pa. The technical atmosphere (98066.5 Pa) stays out of scope so the two never mix silently.
- Inch of mercury
- 3386.389 Pa, the conventional column referenced at 0 degrees Celsius.
- Millimetre of water
- 9.80665 Pa, the conventional basis at standard gravity.
- Pound-force per square inch
- carried at its full derived value 6894.757293168361 Pa. NIST prints 6.894757e3, which is the display rounding of this number.
This converts pressure magnitudes. Moving between gauge and absolute pressure means adding or subtracting the local atmospheric pressure, which depends on where and when you measure, so it stays out of a pure unit converter.
Common conversions
- How many psi in a bar?
- 14.5038 psi (enter 1 with bar selected).
- Convert kPa to psi
- 100 kPa is 14.5038 psi.
- Is torr the same as mmHg?
- No. They diverge in the eighth significant figure; see the note above the export bar.
- What is 1 atm in every unit?
- Enter 1 with atm selected. Choose 8 significant figures to read the exact values.
result = value * k(source) / k(target)
How?
How this is calculated
Every pressure unit is a fixed multiple of the pascal, written here as k, the number of pascals in one of that unit. The tool multiplies your value by the pascals-per-unit of your source unit to get a value in pascals, then divides by the pascals-per-unit of each target unit. No temperature offset enters, unlike a Celsius-to-Fahrenheit step.
The two steps run through the pascal in order rather than collapsing to a single pre-divided ratio, so the last displayed digit is deterministic. Factors come from NIST SP 811, Appendix B.8, with torr and conventional mmHg taken from their own definitions.
Formula: result = value * k(source) / k(target)
Sources
- NIST SP 811, Appendix B.8, Factors for Units Listed Alphabetically. National Institute of Standards and Technology. Retrieved .
- NIST SP 811, Guide for the Use of the International System of Units (SI), 2008 edition. National Institute of Standards and Technology. Retrieved .