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120V Voltage Drop Calculator

Preset for 120 V single-phase — branch circuits, receptacles, lighting and small appliances. A 3% budget at this voltage is 3.6 V.

Voltage Drop
Find Wire Size
Max Length
Advanced — units, power factor, parallel sets, energy cost
PASS
Voltage Drop
Percent Drop
Voltage at Load
Power Lost
Wire Resistance
Ampacity 75°C
0%3% branch5% total8%+

Max one-way distance at 3% (3.6 V) — copper

Size \ Amps15 A20 A30 A50 A100 A
14 AWG3929
12 AWG6247
10 AWG997450
8 AWG1571187947
6 AWG24418312273
4 AWG390292195117
3 AWG49036724514773
2 AWG61946430918693
1 AWG779584390234117
1/0 AWG984738492295148
2/0 AWG1241931620372186
3/0 AWG15671175783470235
4/0 AWG19741480987592296

Cells are blank where the size is below the 75 °C ampacity for that load.

Frequently Asked Questions

What is 3% of 120 volts?

3.6 V — the recommended maximum branch-circuit drop at this voltage. The 5% total budget is 6.0 V.

Built & maintained by Murugan Vellaichamy · Every calculation verified against NEC Chapter 9 Table 8 & Table 310.16 published values · Informational reference — not engineering advice