Voltage Drop Calculator
Calculate voltage drop over a wire run.
How It Works
Drop (V) = (2 × 12.9 × Current × Distance) ÷ cmil. Drop % = Drop ÷ Voltage × 100.
Example
20 A over 100 ft of 12 AWG at 120 V: 7.9 V drop ≈ 6.6%.
Frequently Asked Questions
What is an acceptable voltage drop?
NEC recommends no more than 3% on a branch circuit and 5% total from the service.
Which wire sizes are in the list?
Standard AWG sizes from 14 AWG up to 4/0 are included in the lookup table.
How do I fix excessive drop?
Use a larger wire, shorten the run, or raise the circuit voltage.