Convert Millibars to Decibars

Formula

dbar = mbar ÷ 100

Derivation from SI units:

• 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
• 1 dbar = 10⁻¹ bar = 10⁴ Pa
• 1 mbar = 100 Pa ÷ 10000 Pa per dbar = 0.01 dbar

Both units are defined exactly, so the factor is exact. Millibar definition: millibar; Decibar definition: decibar.

Worked examples

1. A reading of 20 mbar converts to 0.2 dbar.
   20 mbar × 0.01 = 0.2 dbar
2. A value of 900 mbar is 9 dbar.
   900 mbar × 0.01 = 9 dbar

Where it's used

Millibars are used for weather maps and barometers (sea level ≈ 1013 mbar), 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.

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, "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.