Circular Mil Area Calculator
Calculate wire cross-sectional area in circular mils, square inches, and square millimeters from diameter in mils or AWG gauge number.
Circular Mil Area
A circular mil (cmil) is a unit of area used in the United States for measuring wire cross-sections. One circular mil is the area of a circle exactly 1 mil (0.001 inch) in diameter. The unit simplifies wire sizing because you skip the π/4 factor in calculations.
Formulas
| Output | Formula |
|---|---|
| Circular mils | A = d² (where d is diameter in mils) |
| Square inches | A = π × (d / 2000)² |
| Square mm | A = π × (d × 0.0254 / 2)² |
Key Relationship
1 circular mil = (π/4) square mils = 5.0671 × 10⁻⁴ mm²
AWG to Diameter Reference
| AWG | Diameter (mils) | Area (cmil) | Typical Use |
|---|---|---|---|
| 0000 (4/0) | 460.0 | 211,600 | Heavy feeder |
| 2/0 | 364.8 | 133,100 | Service entrance |
| 1 | 289.3 | 83,690 | Branch circuit |
| 4 | 204.3 | 41,740 | Sub-panel feed |
| 10 | 101.9 | 10,380 | Household circuit |
| 14 | 64.08 | 4,107 | Lighting circuit |
Current Capacity
Wire ampacity is proportional to circular mil area. A rule of thumb: allow 700–1000 cmil per ampere for copper conductors in free air. Always consult NEC tables for code-compliant installations.
AWG Formula
For AWG gauge n: diameter (mils) = 92^((36-n)/39) × 5 This calculator accepts either diameter in mils or AWG gauge as input.
How we build and check this calculator
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