Square Millimeters to Square Centimeters (mm² to cm²)

1 square millimeter equals 0.01 square centimeters exactly.

1 square millimeter = 0.01 square centimeters

How to convert square millimeters to square centimeters

To convert square millimeters to square centimeters, multiply the number of square millimeters by 0.01. This factor is exact. To go the other way, multiply square centimeters by 100.

square centimeters = square millimeters × 0.01

Example: 10 square millimeters = 0.1 square centimeters.

About these units

Square Millimeter (mm²)

Metric (SI)Current unit

A square one millimeter on a side. Used for the cross-section of wires and small parts.

Gauss gets the credit for putting the millimeter at the base of a scientific measuring system. His 1832 proposal for absolute units used the millimeter, milligram and second, although the centimeter-based CGS system later won out among scientists. The square millimeter is a one-thousandth-by-one-thousandth square of a meter, so it takes a million of them to make a square meter, and it has no famous inventor of its own.

Electricians know it best. Wire and cable sizes are given as the cross-sectional area of the copper conductor, and the standard sizes listed for UK domestic wiring are 1, 1.5, 2.5, 4, 6 and 10 mm². Twin and earth cable of 2.5 mm² typically serves sockets on a 16 A radial or 32 A ring circuit, 1 mm² serves lighting on a 6 A breaker, and 4 mm² feeds a cooker or shower. Conductor size depends on current capacity and allowed voltage drop, not on voltage alone. One square inch is exactly 645.16 mm², so small parts in either system compare easily.

1 square millimeter = 0.000001 square meters (exactly).

Sources: Wikipedia: Electrical wiring in the United Kingdom; Wikipedia: Centimetre-gram-second system of units; Wikipedia: Square metre

Square Centimeter (cm²)

Metric (SI)Current unit

A square one centimeter on a side; 1/10,000 of a square meter.

Physicists, rather than surveyors, put the centimeter at the center of a measuring system. Carl Friedrich Gauss proposed absolute units based on length, mass and time in 1832, choosing the millimeter, and in 1873 a British Association committee including James Clerk Maxwell and William Thomson (Lord Kelvin) recommended the centimeter, gram and second instead. In that CGS system the square centimeter turns up inside derived units, such as the stokes of kinematic viscosity, defined as one square centimeter per second.

A square centimeter is one ten-thousandth of a square meter, so 10,000 of them fill a square meter. It is a natural size for small flat things: a square inch is exactly 6.4516 cm², and a square foot is exactly 929.0304 cm². Because the CGS system defined force and pressure with the centimeter, the dyne per square centimeter became its unit of pressure, called the barye, which equals 0.1 pascal. SI practice prefers the square meter for large areas and the square millimeter for very small ones.

1 square centimeter = 0.0001 square meters (exactly).

Sources: Wikipedia: Centimetre-gram-second system of units; Wikipedia: Square centimetre; NIST Guide to the SI, Appendix B.8: conversion factors

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