Convert Millimeters of Mercury to Centimeters of Water

Formula

cmH₂O = mmHg × 1.35951

Derivation from SI units:

• 1 mmHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.001 m = 133.322387415 Pa
• 1 cmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.01 m = 98.0665 Pa
• 1 mmHg = 133.322387415 Pa ÷ 98.0665 Pa per cmH₂O = 1.35951 cmH₂O

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

Worked examples

1. An intracranial pressure of 20 mmHg is 27.1902 cmH₂O.
   20 mmHg × 1.35951 = 27.1902 cmH₂O
2. A pressure of 5 mmHg equals 6.79755 cmH₂O.
   5 mmHg × 1.35951 = 6.79755 cmH₂O

Where it's used

Vascular pressures in mmHg are converted to cmH₂O when relating them to respiratory or cerebrospinal-fluid pressures measured with water manometers.

Millimeter of Mercury 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 mercury, conventional (mmHg)".
• 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.