AWG to mm² and Diameter Table with Ampacity Quick Reference
AWG ↔ mm² ↔ diameter ↔ resistance table with NEC 310.16 ampacity and temperature / bundling correction.
AWG table
Ampacity columns: NEC (NFPA 70) Table 310.16, copper conductors, not more than three current-carrying conductors in a raceway, cable or directly buried, 30 °C ambient. NEC gives no values below AWG 14 (thinner wire). Overcurrent protection limits in NEC 240.4(D) still apply to AWG 14, 12 and 10.
Automotive, appliance and harness wire is rated differently (ISO 6722, SAE J1128, UL 758 … depend on insulation temperature class, bundle size and duty cycle). Those ratings are not tabulated here — use the wire datasheet.
Correction factors
Corrected ampacity
Temperature correction = √((Tc − Ta) / (Tc − 30)), which is how NEC Table 310.15(B)(1) is derived (Tc = 60, 75 or 90 °C). Conductor-count adjustment per NEC 310.15(C)(1): 4–6 → 80 %, 7–9 → 70 %, 10–20 → 50 %, 21–30 → 45 %, 31–40 → 40 %, 41 and more → 35 %.
Combine conductors
Adds the cross-sections of the conductors. A real terminal or splice has its own limits on the number and sizes of wires — use the terminal datasheet.
Frequently asked questions
How is the AWG wire diameter calculated?
The American Wire Gauge is defined by a formula: diameter in mm = 0.127 × 92^((36 − n) / 39) for gauge n. For example AWG 20 is about 0.81 mm (0.52 mm²), AWG 18 about 1.02 mm (0.82 mm²) and AWG 16 about 1.29 mm (1.31 mm²).
Can I use a wire’s ampacity as the current rating of a connector?
No. Wire ampacity depends on insulation temperature rating, bundling and ambient temperature, while a connector’s current rating is set by its contacts, housing and the temperature rise its manufacturer tests for. Use the lower of the two, and take the connector value from its datasheet.
For preliminary assessment only — the final decision must follow the manufacturer’s datasheet and the applicable NEC / IEC / UL standards. Results are calculated from the standard formulas stated on this page and are for design estimates only. They are not a rating of any specific part — always confirm current, voltage, temperature and environment limits against the manufacturer’s datasheet for the part you intend to use.
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