Convert Millimeters of Mercury to Inches of Mercury

Formula

inHg = mmHg × 0.03937007874016

or inHg = mmHg ÷ 25.4

Derivation from SI units:

• 1 mmHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.001 m = 133.322387415 Pa
• 1 inHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.0254 m = 3386.388640341 Pa
• 1 mmHg = 133.322387415 Pa ÷ 3386.388640341 Pa per inHg = 0.03937007874016 inHg

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

Worked examples

1. A reading of 80 mmHg converts to 3.149606299 inHg.
   80 mmHg × 0.03937007874 = 3.149606299 inHg
2. A value of 160 mmHg is 6.299212598 inHg.
   160 mmHg × 0.03937007874 = 6.299212598 inHg

Where it's used

Millimeters of Mercury are used for blood pressure (e.g. 120/80 mmHg), while inches of mercury appear in aircraft altimeter settings (standard 29.92 inHg). Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Millimeter 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, "millimeter of mercury, conventional (mmHg)".
• 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.