Free Voltage Drop Calculator
Calculate exact voltage drop across a copper conductor run given amperage, distance, and wire gauge area.
A
ft
CM
V
Voltage Drop
4.96 V
Drop Percentage0.00 %
Voltage at Load115.0 V
Voltage Drop vs Current
Voltage Drop Formula
Vdrop = 2 x K x I x D / CM
K is 10.8 for copper (12.9 for aluminum), I is current in amps, D is one-way distance, and CM is the wire cross-section in circular mils. The factor of 2 accounts for the round-trip path.
Example Calculation
20A on 12 AWG (6,530 CM) copper over 75 ft at 120V.
- 01Vdrop = 2 x 10.8 x 20 x 75 / 6530 = 4.96V
- 02Percentage = 4.96 / 120 x 100 = 4.14%
- 03Voltage at load = 120 - 4.96 = 115.0V
- 04This exceeds 3%; consider upsizing to 10 AWG.
Frequently Asked Questions
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