Convert Millibars to Centimeters of Water

Formula

cmH₂O = mbar × 1.019716212978

Derivation from SI units:

• 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
• 1 cmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.01 m = 98.0665 Pa
• 1 mbar = 100 Pa ÷ 98.0665 Pa per cmH₂O = 1.019716212978 cmH₂O

Both units are defined exactly, so the factor is exact. Millibar definition: millibar; Centimeter of Water definition: centimeter of water.

Worked examples

1. A reading of 20 mbar converts to 20.39432426 cmH₂O.
   20 mbar × 1.019716213 = 20.39432426 cmH₂O
2. A value of 900 mbar is 917.7445917 cmH₂O.
   900 mbar × 1.019716213 = 917.7445917 cmH₂O

Where it's used

Millibars are used for weather maps and barometers (sea level ≈ 1013 mbar), while centimeters of water appear in mechanical ventilation (PEEP 5–10 cmH₂O, plateau pressure under 30 cmH₂O). Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Millibar to other pressure units

Frequently asked questions

Sources

• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "millibar".
• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "centimeter of water, conventional (cmH2O)".

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.