Convert Inches of Water to Decibars

Formula

dbar = inH₂O × 0.024908891

or dbar = inH₂O ÷ 40.14630759756

Derivation from SI units:

• 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa
• 1 dbar = 10⁻¹ bar = 10⁴ Pa
• 1 inH₂O = 249.08891 Pa ÷ 10000 Pa per dbar = 0.024908891 dbar

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

Worked examples

1. A reading of 0.3 inH₂O converts to 0.0074726673 dbar.
   0.3 inH₂O × 0.024908891 = 0.0074726673 dbar
2. A value of 3 inH₂O is 0.074726673 dbar.
   3 inH₂O × 0.024908891 = 0.074726673 dbar

Where it's used

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

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, "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.