How this calculator works
A square centimetre is a square one centimetre on each side, and a square millimetre is one millimetre on each side. Since one centimetre is exactly ten millimetres, a square centimetre contains ten rows of ten square millimetres, or 100 mm2. The factor of 100 is exact, unlike factors that mix metric and imperial units. Engineers use mm2 for cable cross-sections and small machined faces, and cm2 for larger plan areas and material samples.
Formula
mm2 = cm2 x 100. cm2 = mm2 / 100. Equivalently, 1 cm2 = 0.0001 m2 and 1 mm2 = 0.000001 m2, so 0.0001 / 0.000001 = 100.
Worked example
1 cm2 = 100 mm2. 2.5 cm2 = 250 mm2. 0.5 cm2 = 50 mm2. 100 cm2 = 10,000 mm2. 1,000 cm2 = 100,000 mm2. 100 mm2 = 1 cm2. A cable listed at 2.5 mm2 is 0.025 cm2.
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Frequently asked questions
Why is the factor 100 and not 10?
Area scales with the square of length. One centimetre is ten millimetres, so a square of one centimetre by one centimetre is ten by ten millimetres, which is 100 square millimetres.
Can I enter a fractional square centimetre?
Yes. The inputs accept decimals, so 0.25 cm2 returns 25 mm2. Small cable and component areas are usually given with one or two decimal places.
How do square millimetres relate to square metres?
One square metre is 10,000 cm2, and one square metre is 1,000,000 mm2. The table shows square metres so you can compare the small units with the SI base unit.
Is this the same as a millimetre of cable diameter?
No. A cable given in mm2 is quoted by conductor cross-sectional area, not by diameter. A round conductor of 2.5 mm2 has a diameter of about 1.78 mm.