Convert Inches of Mercury to Torr

Formula

Torr = inHg × 25.40000361864

Derivation from SI units:

• 1 inHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.0254 m = 3386.388640341 Pa
• 1 Torr = 101325/760 Pa = 133.3223684 Pa (1/760 of a standard atmosphere)
• 1 inHg = 3386.388640341 Pa ÷ 133.3223684211 Pa per Torr = 25.40000361864 Torr

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

Worked examples

1. A reading of 15 inHg converts to 381.0000543 Torr.
   15 inHg × 25.40000362 = 381.0000543 Torr
2. A value of 29 inHg is 736.6001049 Torr.
   29 inHg × 25.40000362 = 736.6001049 Torr

Where it's used

Inches of Mercury are used for aircraft altimeter settings (standard 29.92 inHg), while torr appear in vacuum technology and vacuum gauges. Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

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, "torr (Torr)".

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