square inch to square millimeter
Convert square inch (in²) to square millimeter (mm²). Use an editable area converter, conversion formula, and reference table.
1 in² = 645.16 mm²
Conversion formula
One square inch equals 645.16 square millimeter. Multiply your value in square inch by this factor to get square millimeter. For the reverse conversion, divide by the same factor.
Worked example
To convert 5 square inch:5 × 645.16 = 3,225.8 mm²
Conversion table
| square inch (in²) | square millimeter (mm²) |
|---|---|
| 0.01 | 6.4516 |
| 0.1 | 64.516 |
| 1 | 645.16 |
| 2 | 1,290.32 |
| 5 | 3,225.8 |
| 10 | 6,451.6 |
| 25 | 16,129 |
| 50 | 32,258 |
| 100 | 64,516 |
| 1000 | 645,160 |
About these measurements
Area measures a surface in two dimensions.
The base reference used here is the square meter. One square inch is 0.00064516 base units; one square millimeter is 0.000001 base units.
Important distinctions
Square a length factor to convert an area. Units with equal factors can have different conventional uses.
Precision
The converter uses stored conversion factors and floating-point arithmetic. Results display up to ten significant digits, switching to scientific notation for very small or large values. Keep the precision of your original measurement when reporting results.
Common questions
How do I convert in² to mm²?
Multiply the quantity in in² by 645.16. You can also type the value into the converter above.
Can I reverse the conversion?
Yes. Use the swap button or open the square millimeter to square inch converter.
Reference
NIST Guide to the SI — conversion factors and prefix conventions. SI prefixes scale units by powers of ten; the dimension-specific notes above describe the assumptions used on this page.
