Wire Size Calculator — Ampacity

How NEC 310.16 ampacity works

NEC Table 310.16 lists the maximum allowable ampacity for insulated conductors rated up to 2000 V based on conductor material and the temperature rating of the insulation. The table has three columns — 60°C, 75°C, and 90°C — corresponding to the temperature rating of the wire's insulation (e.g., THHN is 90°C, THWN is 75°C). Aluminum is not listed for 14 AWG, and generally carries less current than the same-size copper conductor at every temperature column.

Even when you use 90°C-rated wire, the termination temperature rating at the device or panelboard typically limits the effective ampacity to the 75°C column per NEC 110.14(C). This calculator finds the smallest conductor whose Table 310.16 ampacity meets or exceeds your load. It does not apply ambient-temperature correction factors (NEC 310.15(B)(1)) or the conductor-bundling derating factor (NEC 310.15(C)) — apply those adjustments separately before selecting the final wire size in the field.