CPAP tools
CPAP Pressure Unit Converter
CPAP pressure in the United States is almost always written in centimeters of water (cm H2O). Some devices and international documents use hectopascals (hPa) or millibars (mbar). One cm H2O equals 0.980665 hPa, so the numbers are close but not identical. Enter either value to convert.
How it works
1 cm H2O = 98.0665 Pa = 0.980665 hPa (1 hPa = 1 mbar). 1 mmHg = 133.322 Pa and 1 psi = 6,894.757 Pa. To go from hPa to cm H2O, divide by 0.980665.
Example
10 cm H2O x 0.980665 = 9.81 hPa (9.81 mbar), 0.98 kPa, 7.36 mmHg or 0.14 psi.
Assumptions and limits
- Uses the conventional cm H2O value (water at 4 degrees Celsius, standard gravity) listed by NIST.
- Do not change your prescribed pressure based on a conversion; pressure settings are set by your clinician.
Frequently asked questions
Is 1 hPa the same as 1 cm H2O?
Almost. 1 cm H2O is 0.98 hPa, a 2 percent difference. At typical CPAP pressures the gap is a fraction of a unit, but use the exact unit your prescription is written in.
What is a typical CPAP pressure?
Prescribed pressures commonly fall somewhere between about 4 and 20 cm H2O, the usual adjustable range of CPAP machines. Your own pressure comes from a titration study or from auto CPAP data reviewed by your clinician.
Are hPa and mbar the same?
Yes. One hectopascal equals one millibar.
Sources
Tools and screening scores are general information. They cannot diagnose or rule out a sleep disorder. Read our medical disclaimer.