Convert Millimeters of Water to Centimeters of Water

Formula

cmH₂O = mmH₂O ÷ 10

Derivation from SI units:

• 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa
• 1 cmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.01 m = 98.0665 Pa
• 1 mmH₂O = 9.80665 Pa ÷ 98.0665 Pa per cmH₂O = 0.1 cmH₂O

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

Worked examples

1. A reading of 25 mmH₂O converts to 2.5 cmH₂O.
   25 mmH₂O × 0.1 = 2.5 cmH₂O
2. A value of 250 mmH₂O is 25 cmH₂O.
   250 mmH₂O × 0.1 = 25 cmH₂O

Where it's used

Millimeters of Water are used for fan static pressure and duct design in Asia and Europe, 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.

Millimeter 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, "millimeter of water, conventional (mmH2O)".
• 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.