How the converter works
Every unit is converted through the pascal (Pa), the SI unit of pressure, using a fixed factor per unit. Type a value into any field; all others update at once, and the field you typed in stays highlighted as the source. Results are shown to seven significant figures, which is more than any industrial pressure measurement can resolve.
The conversion factors
| Unit | Pascals | Definition |
|---|---|---|
| bar | 100 000 | Exact by definition |
| mbar, hPa | 100 | Exact; the same size |
| kPa, MPa | 1 000, 1 000 000 | SI multiples |
| psi | 6 894.757 | Pound-force per square inch |
| psf | 47.880 | Pound-force per square foot (psi ÷ 144) |
| atm | 101 325 | Standard atmosphere, exact |
| Torr | 133.322 | 1/760 of an atmosphere, exact |
| mmHg | 133.322 387 | Mercury at 0 °C, standard gravity |
| inHg | 3 386.389 | Mercury at 0 °C |
| kgf/cm² | 98 066.5 | Exact, also called “technical atmosphere” (at) |
| mmH₂O, mH₂O | 9.80665, 9 806.65 | Water at 4 °C, standard gravity |
| inH₂O | 249.089 | Water at 4 °C |
Torr and mmHg are almost but not exactly equal; they differ by about 0.000015 %.
Quick reference
- 1 bar = 14.5038 psi = 100 kPa = 0.1 MPa
- 1 psi = 0.0689476 bar = 6.89476 kPa
- 1 MPa = 10 bar = 145.038 psi
- 1 atm = 1.01325 bar = 14.6959 psi = 760 Torr
- 1 kgf/cm² = 0.980665 bar = 14.2233 psi
- 1 inH₂O = 249.089 Pa = 2.49089 mbar
For the most common pairs there are dedicated pages with tables, for example bar to psi, psi to bar, MPa to psi, kPa to psi, inH₂O to Pa and kgf/cm² to bar.
Gauge, absolute and differential pressure
Pressure units don’t say what the pressure is measured against:
- Gauge pressure (psig, barg) is relative to the local atmosphere. Most process instruments read gauge.
- Absolute pressure (psia, bara) is relative to vacuum. Vacuum gauges, barometers and many level calculations need absolute.
- Differential pressure is the difference between two process points, such as across a filter or an orifice plate.
To convert gauge to absolute, add the local atmospheric pressure, which is 1.01325 bar (14.696 psi) at sea level by convention but varies with altitude and weather. Converting units with this tool does not change the reference; 10 barg is 145.04 psig.
Water columns and temperature
Water-column units depend on the density of water, and that depends on temperature. This converter uses water at 4 °C (maximum density) and standard gravity, the most common convention. Some instruments and standards use water at 20 °C or 60 °F, which gives values about 0.1 to 0.2 % different. For low-range differential pressure transmitters in inH₂O, check which convention the transmitter uses.
Common mistakes
Mixing up psi and psia/psig. The unit conversion is the same, but the reference matters when comparing readings.
Using kg/cm² as a mass unit. The unit is kilogram-force per square centimetre; 1 kgf/cm² is 0.980665 bar, not 1 bar.
Assuming mbar and hPa are different. They are identical; meteorology uses hPa, industry mostly mbar.
Frequently asked questions
Why does the converter show so many digits?
To avoid rounding errors when converting back and forth. Round to the precision of your instrument.
Is there a gauge-to-absolute option?
No; add atmospheric pressure separately. Units don’t change the reference.
Can I share a conversion?
Yes. “Copy link” opens the converter with your value and unit already entered.
Which transmitter accuracy do I need?
Use the pressure transmitter accuracy calculator to combine reference accuracy, temperature effect and drift for your range.