Convert Millibars to Millimeters of Mercury

Formula

mmHg = mbar × 0.7500615758457

or mmHg = mbar ÷ 1.33322387415

Derivation from SI units:

• 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
• 1 mmHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.001 m = 133.322387415 Pa
• 1 mbar = 100 Pa ÷ 133.322387415 Pa per mmHg = 0.7500615758457 mmHg

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

Worked examples

1. A reading of 20 mbar converts to 15.00123152 mmHg.
   20 mbar × 0.7500615758 = 15.00123152 mmHg
2. A value of 900 mbar is 675.0554183 mmHg.
   900 mbar × 0.7500615758 = 675.0554183 mmHg

Where it's used

Millibars are used for weather maps and barometers (sea level ≈ 1013 mbar), while millimeters of mercury appear in blood pressure (e.g. 120/80 mmHg). 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, "millimeter of mercury, conventional (mmHg)".

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