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CPAP Pressure Unit Converter
CPAP pressures are set in centimeters of water (cm H2O), but some manuals, altitude specs and European devices use hPa or mbar. Enter a pressure in cm H2O to see it in other units. This is a unit converter only; your prescribed pressure is set by your clinician.
Formula
NIST lists 1 conventional centimeter of water (cm H2O) as 98.0665 Pa, and 1 psi as 6,894.757 Pa. So Pa = cm H2O x 98.0665; hPa = Pa / 100; mbar equals hPa; kPa = Pa / 1000; psi = Pa / 6,894.757.
Rule of thumb: 1 cm H2O is about 0.98 hPa or mbar, so the numbers are close but not equal.
Worked example
10 cm H2O x 98.0665 = 980.665 Pa = 9.81 hPa = 9.81 mbar = 0.98 kPa. In psi: 980.665 / 6,894.757 = 0.142 psi.
Assumptions and limits
- Uses the conventional cm H2O (standard gravity), which is the one used for medical device pressures.
- Do not use this to change your therapy settings; pressure changes go through your prescribing clinician.
Frequently asked questions
Is cm H2O the same as hPa?
Almost: 1 cm H2O is 0.980665 hPa. A setting of 10 cm H2O is 9.81 hPa. The difference matters when comparing specs, not in daily use.
What is 20 cm H2O in psi?
20 x 98.0665 = 1,961.33 Pa, divided by 6,894.757 gives about 0.28 psi. CPAP pressures are very low compared with tire or tank pressures.
Why does my machine's altitude spec use hPa?
Air pressure for altitude is normally given in hPa. The AirSense 11 user guide, for example, lists an operating range of 1060 to 700 hPa, which is a description of the surrounding air, not your therapy pressure.
Sources
Last reviewed October 11, 2026. How we research · Report an error