Wire Size Calculator
Find the correct AWG wire gauge for your circuit based on current, voltage, distance, and maximum voltage drop. Supports copper and aluminum conductors.
Frequently Asked Questions
How do I determine wire size?
Consider three factors: (1) Ampacity — the wire must safely carry the current per NEC Table 310.16; (2) Voltage drop — should stay ≤3% for branch circuits; (3) Distance — longer runs need larger wire to keep voltage drop acceptable.
What size wire do I need for 30 amps?
Minimum 10 AWG copper or 8 AWG aluminum per NEC Table 310.16 (60°C). For runs over 50 feet at 120V, you may need 8 AWG copper to stay within 3% voltage drop.
Does wire length affect wire size?
Yes. Voltage drop is directly proportional to wire length. A 100-foot run may need a wire gauge 1–2 sizes larger than a 25-foot run for the same current and voltage drop target.
AWG Wire Size Reference Table
| AWG | Diameter (in) | Max Amps (Cu, 60°C) | Resistance (Ω/1000ft) |
|---|---|---|---|
| 14 | 0.064 | 15 | 3.14 |
| 12 | 0.081 | 20 | 1.98 |
| 10 | 0.102 | 30 | 1.24 |
| 8 | 0.128 | 40 | 0.778 |
| 6 | 0.162 | 55 | 0.491 |
| 4 | 0.204 | 70 | 0.308 |
| 2 | 0.258 | 95 | 0.194 |
| 1/0 | 0.325 | 125 | 0.122 |
| 2/0 | 0.365 | 145 | 0.0967 |
| 4/0 | 0.460 | 195 | 0.0608 |
Related Calculators
- Voltage Drop Calculator — calculate exact voltage drop for a specific wire gauge
- Watts / Amps / Volts Calculator
- Ohm's Law Calculator (V/A/W/Ω)
Wire ampacity from NEC Table 310.16 (60°C column). Resistance values from NEC Chapter 9, Table 8 at 75°C. Always consult a licensed electrician for actual installations.