mm²

square millimeter

Areaexact by definition

The square millimetre is the area of a square one millimetre on a side, exactly 10⁻⁶ m². It is the standard unit for cross-sections in engineering: cable conductor sizes, bolt stress areas and steel section properties are all quoted in mm². The factor is exact by definition.

Watch out: Stress in mm²-based work usually appears as N/mm², which is numerically identical to the megapascal. A steel with a yield of 355 N/mm² is a 355 MPa steel, not a different number.

1 mm² 0.000001 m²