Convert Millimeters of Water to Millibars

Formula

mbar = mmH₂O × 0.0980665

or mbar = mmH₂O ÷ 10.19716212978

Derivation from SI units:

• 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa
• 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
• 1 mmH₂O = 9.80665 Pa ÷ 100 Pa per mbar = 0.0980665 mbar

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

Worked examples

1. A reading of 25 mmH₂O converts to 2.4516625 mbar.
   25 mmH₂O × 0.0980665 = 2.4516625 mbar
2. A value of 250 mmH₂O is 24.516625 mbar.
   250 mmH₂O × 0.0980665 = 24.516625 mbar

Where it's used

Millimeters of Water are used for fan static pressure and duct design in Asia and Europe, while millibars appear in weather maps and barometers (sea level ≈ 1013 mbar). 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, "millibar".

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