Wire Voltage Drop Calculator
Voltage drop over a wire run by length and gauge.
Enter your values
ⓘ Live results
Results
- Voltage drop
- 3.14 V
- Percent drop
- 2.62%
- Voltage at load
- 116.86 V
- Status
- Within recommended 3% limit
Quick answer
Voltage drop = 2 x length x current x resistance per foot (for round-trip circuits).
Vdrop = 2 L I R_per_ft
How to use the Wire Voltage Drop Calculator
- 1Enter the one-way wire length, load current and the wire's resistance per 1000 ft (from an ampacity table).
- 2Enter the supply voltage.
- 3Check the percent drop against the common 3% design guideline.
Worked example
Using the values the calculator loads with:
Inputs
- One-way length50 ft
- Current10 A
- Resistance per 1000 ft3.14 ohms (12 AWG copper default)
- Supply voltage120 V
Results
- Voltage drop3.14 V
- Percent drop2.62%
- Voltage at load116.86 V
- StatusWithin recommended 3% limit
Frequently asked questions
Why multiply length by 2?
Current travels out and back through the circuit, so both conductors contribute resistance.
What if drop is too high?
Use a thicker (lower AWG number) wire or shorten the run to bring the drop back under 3%.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.