Square inches and square centimeters
A square inch is a square 1 inch on each side: exactly 6.4516 square centimeters. Small surfaces such as photos, circuit boards and tire contact patches, and pressure in psi (pounds per square inch), use it.
A square centimeter is one ten-thousandth of a square meter. Small surfaces such as labels, tiles, wounds and electronic components are measured in square centimeters.
Worked example
Convert 16 in²: 16 × 6.4516 = 103.2256, so 16 square inches is 103.2256 square centimeters. Likewise 20 in² = 129.032 cm².
Estimating in your head
Multiply by 6.5 for a quick figure; it is off by about 0.8%. For 16 in² that gives 104 cm², against 103.226 exactly.
Going the other way
To convert square centimeters to square inches, divide by 6.4516 (or multiply by 0.155000310001).
How this works
cm² = in² × 6.4516
1 in² = 0.00064516 m² and 1 cm² = 0.0001 m², both by definition, so the factor is their ratio: 6.4516 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many square centimeters are in a square inch?
1 square inch = 6.4516 square centimeters, exactly. The value follows from the unit definitions, so it never changes.
How do I convert square inches to square centimeters?
Multiply by 6.4516. For example, 20 in² × 6.4516 = 129.032 cm².
What is 100 in² in square centimeters?
100 in² = 645.16 cm². The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- Federal Register 59-5442 (1959) — Refinement of values for the yard and the pound
- Wikipedia — Acre
Reviewed Oct 17, 2026 · test vectors fixtures/units/area/square-inches-to-square-cm/