Tool
Wire Gauge & Ampacity
AWG ↔ mm², NEC ampacity (60/75/90 °C, copper or aluminum), and voltage-drop calculation for single-phase, three-phase, and DC circuits.
Ampacity
25 A
NEC 310.16, 75 °C
Load uses 80% of capacity.
Voltage drop
3.18 V
1.32% of 240 V
Target: ≤3% branch / ≤5% feeder + branch (NEC informational FPN 210.19).
Recommended minimum size
14
2.08 mm² · 20 A ampacity
Voltage drop at this size: 2.10%
Selected conductor details
- Size
- 12
- Cross-section
- 3.31 mm² (7 kcmil)
- Diameter
- 0.0808 in (2.05 mm)
- Resistance / kft
- 1.588 Ω/kft
- Resistance at length
- 79.40 mΩ (one-way)
Ampacity for this size (copper)
- 60 °C (TW)
- 20 A
- 75 °C (THW)
- 25 A
- 90 °C (THHN)
- 30 A
- 75 °C aluminum
- 20 A
Base values from NEC Table 310.16, ≤3 current-carrying conductors in a raceway. Apply derating for ambient temperature and conduit fill per NEC 310.15.
Quick AWG reference table
| AWG | mm² | Ø in | Ω/kft (Cu) | 60 °C | 75 °C | 90 °C |
|---|---|---|---|---|---|---|
| 18 | 0.82 | 0.0403 | 6.3850 | 7 | 10 | 14 |
| 16 | 1.31 | 0.0508 | 4.0160 | 10 | 13 | 18 |
| 14 | 2.08 | 0.0641 | 2.5250 | 15 | 20 | 25 |
| 12 | 3.31 | 0.0808 | 1.5880 | 20 | 25 | 30 |
| 10 | 5.26 | 0.1019 | 0.9990 | 30 | 35 | 40 |
| 8 | 8.37 | 0.1285 | 0.6280 | 40 | 50 | 55 |
| 6 | 13.30 | 0.1620 | 0.3950 | 55 | 65 | 75 |
| 4 | 21.15 | 0.2043 | 0.2490 | 70 | 85 | 95 |
| 3 | 26.67 | 0.2294 | 0.1970 | 85 | 100 | 115 |
| 2 | 33.62 | 0.2576 | 0.1560 | 95 | 115 | 130 |
| 1 | 42.41 | 0.2893 | 0.1240 | 110 | 130 | 145 |
| 1/0 | 53.49 | 0.3249 | 0.0983 | 125 | 150 | 170 |
| 2/0 | 67.43 | 0.3648 | 0.0779 | 145 | 175 | 195 |
| 3/0 | 85.01 | 0.4096 | 0.0618 | 165 | 200 | 225 |
| 4/0 | 107.20 | 0.4600 | 0.0490 | 195 | 230 | 260 |
| 250 kcmil | 127.00 | 0.5000 | 0.0415 | 215 | 255 | 290 |
| 300 kcmil | 152.00 | 0.5477 | 0.0346 | 240 | 285 | 320 |
| 350 kcmil | 177.00 | 0.5916 | 0.0297 | 260 | 310 | 350 |
| 400 kcmil | 203.00 | 0.6325 | 0.0260 | 280 | 335 | 380 |
| 500 kcmil | 253.00 | 0.7071 | 0.0208 | 320 | 380 | 430 |
| 600 kcmil | 304.00 | 0.7746 | 0.0173 | 350 | 420 | 475 |
| 750 kcmil | 380.00 | 0.8660 | 0.0139 | 400 | 475 | 535 |
| 1000 kcmil | 507.00 | 1.0000 | 0.0104 | 455 | 545 | 615 |
Values are simplified from NEC Table 310.16 (US) for general-purpose sizing. Always verify against the current code edition, the controlling jurisdiction’s amendments, and the actual cable manufacturer’s datasheet for the installation conditions (ambient temperature, conduit fill, termination ratings).