Find the minimum recommended copper wire gauge for a given current.
Ampacity is the maximum current a wire gauge can safely carry continuously without overheating. This uses the simplified 60°C copper column from the NEC ampacity tables, covering common residential and light-commercial gauges.
Thicker wire (lower AWG number) has more copper cross-section and can safely carry more current — the relationship is inverse to the gauge number.
Real installations also factor in conduit fill, ambient temperature, and run length (see the voltage drop calculator for that last one) — this tool gives the baseline ampacity match, not a full code-compliance check.
An 18A circuit needs at minimum 12 AWG wire, rated for 20A — the next size up from 14 AWG's 15A rating.
Breakers and continuous loads typically require sizing above the bare minimum — a 20A breaker commonly pairs with 12 AWG, not wire rated for exactly 20A with no margin.
No — aluminum has different ampacity ratings than copper for the same gauge, generally lower. This table is copper-specific.
No — this gives a standard baseline reference. Actual code compliance depends on conduit fill, ambient temperature, run length, and local code, which a licensed electrician accounts for.