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Pressure Unit Converter

Convert pressure between mmHg, Torr, kPa, Pa, bar, mbar, atm, psi, inHg and cmH₂O, with the clinical units for blood pressure and ventilator pressures.

Formula

1 atm=101 325 Pa1\ \mathrm{atm} = 101\,325\ \mathrm{Pa}
1 mmHg=133.322387 Pa1\ \mathrm{mmHg} = 133.322387\ \mathrm{Pa}
1 cmH2O=98.0665 Pa1\ \mathrm{cmH_2O} = 98.0665\ \mathrm{Pa}
1 psi=6 894.757 Pa1\ \mathrm{psi} = 6\,894.757\ \mathrm{Pa}
1 bar=100 000 Pa1\ \mathrm{bar} = 100\,000\ \mathrm{Pa}
Pa\text{Pa}
the pascal, the SI unit of pressure (N/m²)
mmHg\text{mmHg}
millimetre of mercury, the unit of blood pressure
cmH2O\mathrm{cmH_2O}
centimetre of water, used for airway and ventilator pressures

How it works

Every unit is converted through the pascal. The atmosphere and the bar are defined exactly; the millimetre of mercury is defined by the height of a column of mercury of a conventional density under standard gravity, and the centimetre of water by a column of water likewise, which fixes each to a number of pascals.

The same pressure is written in different units in different parts of a hospital: a blood pressure in mmHg, an airway pressure in cmH₂O or kPa, a gas supply in kPa or psi. Gauge pressure (relative to the atmosphere) and absolute pressure differ by about 101 kPa; the tool changes units only and does not convert between them.

Worked example

A blood pressure of 120 / 80 mmHg.

  1. 120 mmHg × 133.322 Pa = 15,999 Pa = 16.0 kPa.
  2. 80 mmHg × 133.322 Pa = 10,666 Pa = 10.7 kPa.

120 / 80 mmHg is 16.0 / 10.7 kPa. A pressure of 120 mmHg is 163.1 cmH₂O.

These are the values the calculator opens with, so you can check its output against this example.

Assumptions

  • The conventional definitions of the mmHg and cmH₂O, not the pressure of a real column of mercury or water at a given temperature and gravity.
  • Gauge and absolute pressure are not converted into each other.

Common mistakes

  • Mixing gauge and absolute pressure, for example in a gas supply.
  • Confusing mbar and hPa. They are equal.
  • Treating Torr and mmHg as different in any practical sense. They differ by about one part in seven million.

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