Wire Size & Voltage Drop Calculator
Enter your circuit details and get the minimum wire gauge that carries the load safely and keeps voltage drop within limits. Works for copper and aluminum conductors, DC, single-phase, and three-phase circuits.
How This Calculator Works
The calculator checks two constraints and returns the larger required conductor:
1. Voltage drop. Using the standard formula VD = 2 × K × I × L ÷ CM for DC/single-phase (or 1.732 × K × I × L ÷ CM for three-phase), where K is 12.9 ohm-cmil/ft for copper or 21.2 for aluminum, I is load current, L is one-way length in feet, and CM is the conductor's circular-mil area. The calculator finds the smallest gauge whose voltage drop stays within your chosen limit.
2. Ampacity. The conductor must also carry the load current per NEC Table 310.16 (75°C terminations). If ampacity requires a larger size than voltage drop, the larger size wins.
Results are estimates for typical installations at 30°C ambient with no more than three current-carrying conductors. They do not account for conduit fill, ambient derating, continuous-load factors (125%), motor inrush, or harmonics. Always verify against the NEC and consult a licensed electrician or engineer before purchasing or installing.
