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Area
Square millimeters to Square inches
Convert square millimeters (mm²) to square inches (in²). Type a value below to see the result update instantly. Reference table and formula included.
Calculator
1 mm² = 0.00155 in²
Square millimeters to Square inches Conversion Table
Common values, ready to copy:
| square millimeters | square inches |
|---|---|
| 1 mm² | 0.00155 in² |
| 2 mm² | 0.0031 in² |
| 5 mm² | 0.00775 in² |
| 10 mm² | 0.0155 in² |
| 25 mm² | 0.03875 in² |
| 50 mm² | 0.0775 in² |
| 100 mm² | 0.155 in² |
| 1,000 mm² | 1.55 in² |
Formula
square inches = square millimeters × 1.55000310e-3
Area conversions are derived from length: 1 ft² = (0.3048 m)² = 0.092903 m². 1 acre = 4,046.86 m². 1 hectare = 10,000 m² exactly.
About Square millimeters and Square inches
Square millimeters (mm²): One millimeter squared; useful for small areas like wire cross-sections (in mm²) and circuit board features. Common uses: Electrical engineering (wire gauge in mm²), manufacturing tolerances, and small fabricated parts.
Square inches (in²): One inch squared, or 6.4516 cm² exactly (since the inch is defined as 2.54 cm exactly). Common uses: Small flat areas in US contexts — phone screens, computer chip die sizes, postal stamps, and small fabricated parts.
How the conversion works
Area conversions are derived from length: 1 ft² = (0.3048 m)² = 0.092903 m². 1 acre = 4,046.86 m². 1 hectare = 10,000 m² exactly.
The exact relationship is square inches = square millimeters × 1.55000310e-3, which the calculator at the top of this page applies in both directions. Type into either field and the other updates immediately.
When this conversion matters
Converting between square millimeters and square inches comes up wherever area measurements move between systems — from one country's conventions to another's, from a scientific reference to a practical specification, or from one industry's working unit to another's. The calculator and reference table above cover the everyday range; for unusual values you can type any number into either field.