Convert Inches of Mercury to Newtons per Square Millimetre

Formula

N/mm² = inHg × 0.003386388640341

or N/mm² = 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 N/mm² = 1 N ÷ 10⁻⁶ m² = 10⁶ Pa = 1 MPa
• 1 inHg = 3386.388640341 Pa ÷ 1000000 Pa per N/mm² = 0.003386388640341 N/mm²

Both units are defined exactly, so the factor is exact. Inch of Mercury definition: inch of mercury; Newton per Square Millimetre definition: newton per square millimetre.

Worked examples

1. A reading of 15 inHg converts to 0.05079582961 N/mm².
   15 inHg × 0.00338638864 = 0.05079582961 N/mm²
2. A value of 29 inHg is 0.09820527057 N/mm².
   29 inHg × 0.00338638864 = 0.09820527057 N/mm²

Where it's used

Inches of Mercury are used for aircraft altimeter settings (standard 29.92 inHg), while newtons per square millimetre appear in steel yield and tensile strength (S355: 355 N/mm²). 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 4, coherent derived units with special names.

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