How to Convert Square millimetres to Square inches (mm² to sq in)
Area conversions are everyday maths in Singapore property: HDB flats are listed in square metres while condo listings and PSF prices use square feet. This guide shows how to convert square millimetres into square inches by hand, with examples and a quick-reference table.
The conversion
To convert square millimetres to square inches, multiply the value by 0.0015500031. To go the other way, divide by the same number (or multiply by 645.16). For a quick estimate, multiply by about 0.0016.
Square inches = square millimetres × 0.0015500031
Worked examples
- 3 mm² = 0.00465 sq in
- 12.5 mm² = 0.019375 sq in
- 75 mm² = 0.11625 sq in
Square millimetres to Square inches table
| Square millimetres | Square inches |
|---|---|
| 1 mm² | 0.00155 sq in |
| 2 mm² | 0.0031 sq in |
| 5 mm² | 0.00775 sq in |
| 10 mm² | 0.0155 sq in |
| 20 mm² | 0.031 sq in |
| 25 mm² | 0.03875 sq in |
| 50 mm² | 0.0775 sq in |
| 100 mm² | 0.155 sq in |
| 250 mm² | 0.387501 sq in |
| 500 mm² | 0.775002 sq in |
| 1,000 mm² | 1.55 sq in |
Common questions
Is mm² to sq in exact?
The factors used here are the internationally defined values where they exist; results are rounded for display only.
How do I convert back?
Use the Square inches to Square millimetres converter.
Mistakes to avoid
Forgetting squared and cubed units
Area and volume factors are the length factor squared or cubed, so 1 m² is about 10.76 sq ft, not 3.28.
Dropping the units
A bare number without a unit is easy to misread later. Always write the unit with the result.
Multiplying when you should divide
Converting to a smaller unit gives a bigger number, and converting to a larger unit gives a smaller one. If your answer moves the wrong way, you have inverted the factor.
Background
Unit conversion is simply multiplication by a fixed ratio. The ratio between two units of the same quantity never changes, so once you know it you can convert any value in either direction.
For everyday use, three or four significant figures are usually enough. Engineering, science and trade documents may need more, and rounding should happen only at the end of a calculation.
Many conversion factors are exact by definition. The inch has been defined as exactly 2.54 centimetres since 1959, and the pound as exactly 0.45359237 kilograms, so conversions involving them can be as precise as you need.
For any value, use the Square millimetres to Square inches Converter or browse all area converters.
Run your own numbers: Square millimetres to Square inches Converter