Wire Ampacity Calculator (AWG / mm²)
Safe continuous current for a given wire gauge and insulation rating.
Wire ampacity vs. voltage drop — two different questions
This tool answers "how much current can this wire safely carry" — its ampacity, set by how much heat the conductor generates (I²R) versus how well the insulation and surroundings dissipate it before the insulation overheats. That's a different question from the site's voltage drop calculator, which asks "what gauge do I need to keep the drop under X% over this length" — a resistance/length problem, not a thermal one. A wire can pass the ampacity check and still have too much voltage drop on a long run, or vice versa on a short, high-current run — check both.
Ampacity isn't a clean formula; it comes from standard tables (here, NEC 310.16 for copper conductors) because it depends on the insulation's temperature rating and how the wire is installed. Higher-rated insulation (90°C vs 60°C) tolerates more current in the same conductor size because it can run hotter before degrading. The reference values above assume ≤3 current-carrying conductors in a raceway or cable and 30°C (86°F) ambient — bundle more conductors together, run at a hotter ambient, or load continuously (>3 hours) and you must apply the code's derating factors (or just step up a wire size for margin).
Values
Values from NEC Table 310.16 (14 AWG–4/0, the range that table actually covers). Copper conductor, ≤3 current-carrying conductors in a raceway/cable, 30°C ambient — the standard NEC 310.16 reference condition. Derate for more conductors, higher ambient, or continuous (>3 h) loads.