Convert Millimeters of Water to Decibars

Formula

dbar = mmH₂O × 0.000980665

or dbar = mmH₂O ÷ 1019.716212978

Derivation from SI units:

• 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa
• 1 dbar = 10⁻¹ bar = 10⁴ Pa
• 1 mmH₂O = 9.80665 Pa ÷ 10000 Pa per dbar = 0.000980665 dbar

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

Worked examples

1. A reading of 25 mmH₂O converts to 0.024516625 dbar.
   25 mmH₂O × 0.000980665 = 0.024516625 dbar
2. A value of 250 mmH₂O is 0.24516625 dbar.
   250 mmH₂O × 0.000980665 = 0.24516625 dbar

Where it's used

Millimeters of Water are used for fan static pressure and duct design in Asia and Europe, while decibars appear in oceanography: CTD instruments report sea pressure in dbar. 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, "bar", with SI prefix deci (10⁻¹).

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