Convert Millibars to Inches of Mercury

Formula

inHg = mbar × 0.02952998330101

or inHg = mbar ÷ 33.86388640341

Derivation from SI units:

• 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
• 1 inHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.0254 m = 3386.388640341 Pa
• 1 mbar = 100 Pa ÷ 3386.388640341 Pa per inHg = 0.02952998330101 inHg

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

Worked examples

1. Standard pressure, 1013.25 mbar, is 29.92125558 inHg.
   1013.25 mbar × 0.0295299833 = 29.92125558 inHg
2. A low-pressure system of 990 mbar reads 29.23468347 inHg.
   990 mbar × 0.0295299833 = 29.23468347 inHg

Where it's used

Weather data and altimeter settings in hPa or mbar are converted to inHg for US pilots, barometers and weather reports.

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 mercury, conventional (inHg)".

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