cmil
circular mil
Areaexact by definition
A circular mil is the area of a circle one thou (0.001 in) in diameter, about 5.067 × 10⁻¹⁰ m². Its virtue is that a round conductor's area in circular mils is simply its diameter in thou, squared, with no π to carry: a 100 thou wire is 10,000 cmil.
Watch out: The factor involves π, so it is exact by definition but not a terminating decimal. Do not confuse the circular mil with the square mil, which is π/4 times larger and is what you get if you square the diameter without thinking about the shape.
| 1 cmil | 5.0670748e-10 m² |
Where the unit came from
The unit exists because wire is specified by diameter and sold by cross section, and before calculators the squaring shortcut was worth a great deal. American Wire Gauge tables are still published with a circular mil column.
Solvers that use area