What is a Square Millimeter?

The square millimeter equals one millionth of a square meter (10⁻⁶ m²) and is the precision area unit for electronics, microfabrication, mechanical engineering, and component cross-sections. Wire gauges in electronics specify cross-sectional area in mm² (a 2.5 mm² wire is standard for household lighting circuits). Computer chip die sizes and printed circuit board footprints are measured in mm². The square millimeter relates to the square centimeter (100 mm² = 1 cm²), the square meter (1,000,000 mm² = 1 m²), and the square inch (1 mm² ≈ 0.00155 in²). Engineering tolerances, microscope-image areas, and laser-spot sizes all use this scale. The square millimeter is critical in stress calculations: pressure (N/mm²) and strength (MPa) calculations in mechanical engineering routinely use this unit.

Visual reference for how the square millimeter relates to other area units. Each row links to the full converter for that pair.

• Electrical cable cross-section (e.g. 2.5 mm² copper)
• Microelectronics and semiconductor areas
• Pharmaceutical tablet surface areas

• ✓1 mm² = 0.01 cm² = 10⁻⁶ m².
• ✓Electrical cables: 1 mm² up to 10 A; 2.5 mm² up to 16 A (EU standards).
• ✓Always convert to m² for large structures; mm² for precision parts.

• ✗Using mm² instead of cm² for medium-sized surfaces — clutters figures.
• ✗Confusing mm² with mm — different dimensions.
• ✗Assuming a cable rated at 1.5 mm² is 1.5 mm wide — it is the conductive cross-section.