Voltage Drop Calculator

Calculate voltage drop across electrical wire runs for copper and aluminum conductors. Compare all standard AWG gauges to find the minimum wire size that keeps voltage drop within the NEC-recommended 3% limit.

System Voltage

Conductor Material

Amperage (amps)

Wire Run Distance (ft, one-way)

Wire Gauge

Voltage Drop

7.90 V

6.6% of 120V

Voltage at Load

112.1 V

Using 12 AWG

Power Loss

158.0 W

12 AWG copper

NEC Status

Over 3%

Exceeds NEC recommendation

Wire Gauge	Voltage Drop	NEC Status
14 AWG	12.55V (10.5%)	Exceeds 3%
12 AWG	7.90V (6.6%)	Exceeds 3%
10 AWG	4.97V (4.1%)	Exceeds 3%
8 AWGBest value	3.13V (2.6%)	OK (< 3%)
6 AWG	1.97V (1.6%)	OK (< 3%)
4 AWG	1.24V (1.0%)	OK (< 3%)
2 AWG	0.78V (0.6%)	OK (< 3%)
1/0 AWG	0.49V (0.4%)	OK (< 3%)

Minimum recommended: 8 AWG copper8 AWG is the smallest gauge that keeps voltage drop under 3% (2.6% actual) for a 100 ft run at 20A on 120V copper. This delivers 116.9V at the load with 62.5W of power loss.

This is a simplified estimate for single-phase circuits using the NEC Chapter 9 Table 8 circular mil method. Actual voltage drop depends on conductor temperature, conduit type, power factor, and installation conditions. Consult a licensed electrician for final wire sizing.