Convert Millibars to Inches of Water (60 °F)

Formula

inH₂O (60 °F) = mbar × 0.4018646519852

or inH₂O (60 °F) = mbar ÷ 2.4884

Derivation from SI units:

• 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
• 1 inH₂O (60 °F) ≈ 999.0 kg/m³ × 9.80665 m/s² × 0.0254 m ≈ 248.84 Pa
• 1 mbar = 100 Pa ÷ 248.84 Pa per inH₂O (60 °F) = 0.4018646519852 inH₂O (60 °F)

One unit is a measured value, so the factor is approximate. Millibar definition: millibar; Inch of Water (60 °F) definition: inch of water (60 °F).

Worked examples

1. A reading of 20 mbar converts to 8.03729304 inH₂O (60 °F).
   20 mbar × 0.401864652 = 8.03729304 inH₂O (60 °F)
2. A value of 900 mbar is 361.6781868 inH₂O (60 °F).
   900 mbar × 0.401864652 = 361.6781868 inH₂O (60 °F)

Where it's used

Millibars are used for weather maps and barometers (sea level ≈ 1013 mbar), while inches of water (60 °F) appear in older US gas-industry and flow-meter references. Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Millibar 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, "millibar".
• 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 (60 °F)".

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