WireSizing
Wire gauge reference & calculator

What Wire Size for 125 Amps?

Copper Wire
1/0 AWG
8.2515 mm · 53.4751 mm²
Aluminum Wire
2/0 AWG
9.2658 mm · 67.4309 mm²
Breaker: 125A · Based on NEC Table 310.16 (75°C insulation)

Common Uses for 125A Circuits

Service entrance, large main panels

1/0 AWG Copper — Key Specs

Diameter8.2515 mm (0.324861")
Area53.4751 mm²
Resistance at 20°C0.3224 Ω/km
Weight479.137 kg/km
Ampacity (75°C)125 A

Important: For long wire runs, you may need to upsize the wire to compensate for voltage drop. NEC recommends keeping voltage drop under 3% for branch circuits. Use our voltage drop calculator to check.

Related

1/0 AWG full specifications → Full AWG chart → Wire size calculator → Ampacity tables →