How to convert square inches to square millimeters
To convert a measurement in square inches to square millimeters, multiply the value by 645.16. The conversion factor comes from the relationship between both units and the square meter.
For example, to convert 5 in² to square millimeters: 5 × 645.16 = 3,225.8 mm².
What is a square inch?
A square inch is an imperial and US customary unit of area equal to the area of a square one inch on each side, exactly 6.4516 square centimeters. The square inch is used for small areas in the US and UK, notably in engineering where pressure is measured in pounds per square inch (psi), one of the most common pressure units in the world.
Common uses of square inches include: Pressure measurement (pounds per square inch); Print and display area; Small material and gasket areas; Product surface and packaging specs.
What is a square millimeter?
A square millimeter is a metric unit of area equal to the area of a square one millimeter on each side, or one millionth of a square meter. The square millimeter is the go-to unit for very small cross-sections, most notably the gauge of electrical wires and the area of tiny mechanical components.
Common uses of square millimeters include: Electrical wire cross-section (cable gauge); Precision engineering and machining; Cross-sectional area of small parts; Microscopy and materials science.
Square Inches to square millimeters worked examples
Here are some common values converted:
1 in² = 645.16 mm² 5 in² = 3,225.8 mm² 10 in² = 6,451.6 mm² 50 in² = 32,258 mm² 100 in² = 64,516 mm²
Frequently asked questions
How many square millimeters are in one square inch?
One square inch (in²) equals 645.16 square millimeters (mm²). Multiply any value in square inches by 645.16 to convert to square millimeters.
How do I convert square inches to square millimeters?
Multiply the value in square inches by 645.16. For example, 5 in² × 645.16 = 3,225.8 mm².
How do I convert square millimeters to square inches?
Multiply the value in square millimeters by 0.0015500031, or divide by 645.16. Use the swap button on the converter above to reverse the direction.
Is the square inch to square millimeter conversion exact?
Yes. Area conversions derive from the exact 1959 international definitions of the meter, yard, and foot, so the factors are exact.
What is the formula for square inches to square millimeters?
The formula is: mm² = in² × 645.16. This comes from the definition of both units relative to the square meter.