Convert Inches of Mercury to Millibars

Formula

mbar = inHg × 33.86388640341

Derivation from SI units:

• 1 inHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.0254 m = 3386.388640341 Pa
• 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
• 1 inHg = 3386.388640341 Pa ÷ 100 Pa per mbar = 33.86388640341 mbar

Both units are defined exactly, so the factor is exact. Inch of Mercury definition: inch of mercury; Millibar definition: millibar.

Worked examples

1. A standard altimeter setting of 29.92 inHg is 1013.207481 mbar.
   29.92 inHg × 33.8638864 = 1013.207481 mbar
2. A high-pressure day with 30.12 inHg on the barometer is 1019.980258 mbar.
   30.12 inHg × 33.8638864 = 1019.980258 mbar

Where it's used

US aviation and weather reports use inHg; most other countries use hPa, which equals mbar. Pilots convert altimeter settings when flying between regions.

Inch of Mercury 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 mercury, conventional (inHg)".
• 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.