Wire Gauge Calculator

This calculator computes the required conductor resistance from your maximum acceptable voltage drop, current, and round-trip wire distance, then looks up the thinnest AWG size from a ten-gauge table (14 AWG down to 0 AWG) whose resistance-per-1000ft rating meets that requirement. Switching System Voltage from 120V to 240V shifts the recommendation by about one gauge step (for example 12 AWG to 14 AWG), because it doubles the allowed voltage-drop budget for the same drop percentage. Current and One-Way Distance have a much larger effect on the recommendation: sweeping Current across its full range or One-Way Distance across its full range can each move the recommendation across the entire AWG table, from 14 AWG down to 2 AWG.

Because the AWG table only has ten discrete steps, small changes in Current or Distance often land on the same gauge recommendation as before -- the gauge only jumps when a change is large enough to cross one of the table's resistance thresholds. Total Wire Length is a pure convenience figure: it always equals twice your One-Way Distance (the round trip out and back) and never responds to Current, System Voltage, or Max Voltage Drop. This tool applies the 3% branch-circuit voltage-drop guidance from NFPA 70, the National Electrical Code (NEC), as a rule of thumb, and looks up gauges from the same resistance-per-1000ft values the NEC's own conductor tables are built from; it does not account for ambient temperature derating, conduit fill, or the specific overcurrent protection device, so always verify the final gauge against your local code before purchasing wire.