Pick the right copper wire size from current, run length, and allowed voltage drop
| AWG | Ø mm | mm² | Ampacity | V drop | Drop % |
|---|---|---|---|---|---|
| 0000 (4/0) | 11.684 | 107.22 | 380 A | 0.016 V | 0.13% |
| 000 (3/0) | 10.405 | 85.03 | 328 A | 0.020 V | 0.17% |
| 00 (2/0) | 9.266 | 67.43 | 283 A | 0.026 V | 0.21% |
| 0 (1/0) | 8.251 | 53.47 | 245 A | 0.032 V | 0.27% |
| 1 | 7.348 | 42.41 | 211 A | 0.041 V | 0.34% |
| 2 | 6.544 | 33.63 | 181 A | 0.051 V | 0.43% |
| 4 | 5.189 | 21.15 | 135 A | 0.082 V | 0.68% |
| 6 | 4.115 | 13.30 | 101 A | 0.130 V | 1.08% |
| 8 | 3.264 | 8.37 | 73 A | 0.206 V | 1.72% |
| 10 | 2.588 | 5.26 | 55 A | 0.328 V | 2.73% |
| 12 | 2.053 | 3.31 | 41 A | 0.521 V | 4.34% |
| 14 | 1.628 | 2.08 | 32 A | 0.828 V | 6.90% |
| 16 | 1.291 | 1.31 | 22 A | 1.317 V | 10.98% |
| 18 | 1.024 | 0.82 | 16 A | 2.093 V | 17.44% |
| 20 | 0.812 | 0.52 | 11 A | 3.329 V | 27.74% |
| 22 | 0.644 | 0.33 | 7 A | 5.293 V | 44.11% |
| 24 | 0.511 | 0.21 | 3.5 A | 8.406 V | 70.05% |
| 26 | 0.405 | 0.13 | 2.2 A | 13.383 V | 111.52% |
| 28 | 0.321 | 0.08 | 1.4 A | 21.303 V | 177.52% |
| 30 | 0.255 | 0.05 | 0.86 A | 33.757 V | 281.31% |
Two limits matter: the wire's ampacity (safe continuous current, shown for chassis wiring) and the voltage drop over the round-trip run, computed from copper resistivity (1.724×10⁻⁸ Ω·m at 20 °C). Low-voltage systems (12 V solar, automotive, LED runs) are usually voltage-drop limited, which is why they need surprisingly thick cable. Always follow local electrical codes for mains wiring.
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