Convert Inches of Mercury to Megapascals

Formula

MPa = inHg × 0.003386388640341

or MPa = inHg ÷ 295.2998330101

Derivation from SI units:

• 1 inHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.0254 m = 3386.388640341 Pa
• 1 MPa = 10⁶ Pa = 1 N/mm²
• 1 inHg = 3386.388640341 Pa ÷ 1000000 Pa per MPa = 0.003386388640341 MPa

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

Worked examples

1. A reading of 15 inHg converts to 0.05079582961 MPa.
   15 inHg × 0.00338638864 = 0.05079582961 MPa
2. A value of 29 inHg is 0.09820527057 MPa.
   29 inHg × 0.00338638864 = 0.09820527057 MPa

Where it's used

Inches of Mercury are used for aircraft altimeter settings (standard 29.92 inHg), while megapascals appear in concrete compressive strength (typically 20–50 MPa). 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)".
• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 7, SI prefixes.

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