Convert Inches of Water to Centimeters of Water

Formula

cmH₂O = inH₂O × 2.54

Derivation from SI units:

• 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa
• 1 cmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.01 m = 98.0665 Pa
• 1 inH₂O = 249.08891 Pa ÷ 98.0665 Pa per cmH₂O = 2.54 cmH₂O

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

Worked examples

1. A reading of 0.3 inH₂O converts to 0.762 cmH₂O.
   0.3 inH₂O × 2.54 = 0.762 cmH₂O
2. A value of 3 inH₂O is 7.62 cmH₂O.
   3 inH₂O × 2.54 = 7.62 cmH₂O

Where it's used

Inches of Water are used for HVAC total external static pressure (residential ≈ 0.5 inH₂O), 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.

Inch 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, "inch of water, conventional (inH2O)".
• 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.