Wire Gauge Calculator

Minimum wire size per NEC 310.15 ampacity with derating and voltage drop check

Circuit Parameters

Circuit Amperage (A)

System Voltage

One-Way Circuit Length (ft)

Current-Carrying Conductors in Conduit

Wire Material

Insulation Temperature Rating

THHN/THWN-2 = 90°C · THWN = 75°C · NM-B = 60°C

Minimum Wire Size (NEC Ampacity)

14 AWG

20A derated capacity

Voltage Drop

10.46%

Drop (volts)

12.55V

Voltage at Load

107.4V

✗ Voltage drop exceeds 5% — wire must be upsized

Upsize to 12 AWG → 6.58% drop

30°C ambient, not more than 3 current-carrying conductors in raceway

Gauge	60°C	75°C	90°C
14 AWG	15A	20A	25A
12 AWG	20A	25A	30A
10 AWG	30A	35A	40A
8 AWG	40A	50A	55A
6 AWG	55A	65A	75A
4 AWG	70A	85A	95A
3 AWG	85A	100A	110A
2 AWG	95A	115A	130A
1 AWG	110A	130A	150A
1/0 AWG	125A	150A	170A
2/0 AWG	145A	175A	195A
3/0 AWG	165A	200A	225A
4/0 AWG	195A	230A	260A
250 kcmil	215A	255A	290A
300 kcmil	240A	285A	320A
350 kcmil	260A	310A	350A
400 kcmil	280A	335A	380A
500 kcmil	320A	380A	430A

Conduit derating: 4–6 conductors = 80% · 7–9 = 70% · 10–20 = 50% · 21–30 = 45% · 31–40 = 40%

NEC 210.19(A): Conductor ampacity ≥ non-continuous load + 125% of continuous load

VD formula: VD = (2 × K × I × L) / CM, where K = 12.9 Cu · 21.2 Al