Convert Centimeters of Water to Millimeters of Water

Formula

mmH₂O = cmH₂O × 10

Derivation from SI units:

• 1 cmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.01 m = 98.0665 Pa
• 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa
• 1 cmH₂O = 98.0665 Pa ÷ 9.80665 Pa per mmH₂O = 10 mmH₂O

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

Worked examples

1. A reading of 6 cmH₂O converts to 60 mmH₂O.
   6 cmH₂O × 10 = 60 mmH₂O
2. A value of 30 cmH₂O is 300 mmH₂O.
   30 cmH₂O × 10 = 300 mmH₂O

Where it's used

Centimeters of Water are used for mechanical ventilation (PEEP 5–10 cmH₂O, plateau pressure under 30 cmH₂O), while millimeters of water appear in fan static pressure and duct design in Asia and Europe. Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Centimeter of Water 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, "centimeter of water, conventional (cmH2O)".
• 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, "millimeter of water, conventional (mmH2O)".

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