CPAP pressure units: cm H2O to hPa and mbar

CPAP pressure is usually shown in centimeters of water (cm H2O). Some machines and manuals use hectopascals (hPa) or millibars (mbar). One hPa equals one mbar, and 1 cm H2O equals 0.980665 hPa.

cm H2O	hPa	mbar
4	3.92	3.92
5	4.90	4.90
6	5.88	5.88
7	6.86	6.86
8	7.85	7.85
9	8.83	8.83
10	9.81	9.81
11	10.79	10.79
12	11.77	11.77
13	12.75	12.75
14	13.73	13.73
15	14.71	14.71
16	15.69	15.69
17	16.67	16.67
18	17.65	17.65
19	18.63	18.63
20	19.61	19.61
25	24.52	24.52
30	29.42	29.42

Notes

NIST lists the conventional centimeter of water as 98.0665 Pa (0.980665 hPa). 1 hPa = 100 Pa = 1 mbar.
The difference is about 2%, so manufacturers often print ranges as equivalent; ResMed, for example, lists the AirSense 11 range as 4 to 20 cm H2O (4 to 20 hPa).
To convert hPa or mbar back to cm H2O, divide by 0.980665 (or multiply by about 1.0197).
This table is for reading manuals and reports. Your prescribed pressure is set by your clinician.

Sources

More reference tables

AHI severity scale for adult sleep apnea CPAP mask type comparison CPAP power draw (manufacturer figures)CPAP vs APAP vs BiPAP vs ASV Common HCPCS codes for PAP devices and supplies FAA lithium battery rules for CPAP batteries Medicare PAP supply replacement schedule

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