A walkthrough, end to end.
- 1
Enter wire material, AWG gauge, current (amps), and one-way length.
- 2
Pick single-phase or three-phase.
- 3
See voltage drop, percentage, and end-of-run voltage.
Voltage drop
Vd = (2 × L × I × ρ) / A for single-phase, ×√3 for three-phase. Resistance per AWG is from NEC Chapter 9 Table 8.
What you can do with this.
Long runs
Check if a 100 ft run drops too much voltage.
Solar / EV chargers
Size DC or 240 V AC feeders correctly.
Subpanel feeders
Size between main and subpanel for low loss.
Outdoor lighting
Avoid dim lights at the far end of a run.
Motor circuits
Verify <3% drop on motor branch circuits.
Audio / stage rigs
Avoid voltage sag affecting amplifiers.
Frequently asked.
NEC recommends ≤3% on branch circuits, ≤5% total.
Aluminum has ~1.6× the resistance of copper for the same gauge.
No. All math runs in your browser.
This calculator uses DC resistance. AC adds slight reactance, generally negligible at residential gauges.