How Does This Calculator Work?
The calculator accounts for the round-trip length of the circuit (out and back, hence ×2), multiplies by current and the wire's resistance per 1,000 feet, then converts the result to actual volts dropped.
Long wire runs can lose meaningful voltage before power reaches its destination. This calculator estimates that voltage drop from the circuit's current, the one-way wire length, and the wire's resistance rating.
Example Calculation
Long Run Example
20A circuit, 100 ft one-way run, 3.07 Ω/1000ft wire.
(20×100×2×3.07)/1000 ≈ 12.3V dropped.
Tips
This is an estimate for planning purposes, not a substitute for a licensed electrician's calculations on a real installation — voltage drop over 3% is generally considered problematic for most circuits.