Free Wire Gauge Calculator
Determine the minimum wire gauge (AWG) for a circuit based on amperage and run length to keep voltage drop within limits.
A
ft
%
Max Resistance Allowed
1.800 ohm/kft
Min Circular Mils0 CM
Max Resistance Allowed vs Circuit Amperage
Wire Gauge Selection
CM = 2 x K x I x D / Vdrop
Where K = 10.8 (copper resistivity constant), I is current in amps, D is one-way distance in feet, and Vdrop is the allowable voltage drop in volts. Compare the resulting circular mils to an AWG table to pick the minimum wire size.
Example Calculation
20A circuit, 50 ft run, 120V, 3% max drop.
- 01Allowable drop = 120 x 0.03 = 3.6V
- 02CM = 2 x 10.8 x 20 x 50 / 3.6 = 6,000 CM
- 0312 AWG = 6,530 CM, which satisfies the requirement
- 04Use 12 AWG copper wire.
Frequently Asked Questions
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