Convert Atmospheres to Centimeters of Water

Formula

cmH₂O = atm × 1033.2274528

Derivation from SI units:

• 1 atm = 101 325 Pa (exact, by definition)
• 1 cmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.01 m = 98.0665 Pa
• 1 atm = 101325 Pa ÷ 98.0665 Pa per cmH₂O = 1033.2274528 cmH₂O

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

Worked examples

1. A reading of 1.5 atm converts to 1549.841179 cmH₂O.
   1.5 atm × 1033.227453 = 1549.841179 cmH₂O
2. A value of 10 atm is 10332.27453 cmH₂O.
   10 atm × 1033.227453 = 10332.27453 cmH₂O

Where it's used

Atmospheres are used for chemistry and gas laws (STP and NTP conditions), 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.

Atmosphere 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, "atmosphere, standard (atm)".
• 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.