Convert Newtons per Square Millimetre to psi (N/mm2 to psi)

Formula

psi = N/mm² × 145.0377377302

Derivation from SI units:

• 1 N/mm² = 1 N ÷ 10⁻⁶ m² = 10⁶ Pa = 1 MPa
• 1 psi = 1 lbf/in² = (0.45359237 kg × 9.80665 m/s²) ÷ (0.0254 m)² = 6894.757293168 Pa
• 1 N/mm² = 1000000 Pa ÷ 6894.757293168 Pa per psi = 145.0377377302 psi

Both units are defined exactly, so the factor is exact. Newton per Square Millimetre definition: newton per square millimetre; psi definition: psi.

Worked examples

1. A reading of 30 N/mm² converts to 4351.132132 psi.
   30 N/mm² × 145.0377377 = 4351.132132 psi
2. A value of 275 N/mm² is 39885.37788 psi.
   275 N/mm² × 145.0377377 = 39885.37788 psi

Where it's used

Newtons per Square Millimetre are used for steel yield and tensile strength (S355: 355 N/mm²), while psi appear in tyre pressure in the United States (about 30–35 psi for cars). Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Newton per Square Millimetre to other pressure units

Frequently asked questions

Sources

• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 4, coherent derived units with special names.
• 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, "pound-force per square inch (psi)".

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