Wire Gauge (AWG) Calculator

American Wire Gauge assigns each size a number rather than a diameter, and the two are related by a fixed geometric formula rather than a lookup table someone typed up once — diameter exactly doubles every six gauge steps down, by definition. That formula is what this calculates from, so it holds for every size from 0000 (4/0) down to the finest gauges used in magnet wire, not just a handful of common ones.

Voltage drop is the practical reason gauge matters: every wire has resistance, and a real length of it drops a small but non-trivial amount of voltage under load — enough, over a long enough run at a high enough current, to dim lights or undervolt equipment at the far end. The common rule of thumb is to keep drop under 3% of the supply voltage for a branch circuit, which this checks against automatically.

Ampacity — how much current a gauge can safely carry — is presented differently from the rest, deliberately. Diameter, area and resistance are geometry and physics; they are exact regardless of context. Ampacity depends on insulation type, ambient temperature, how many conductors are bundled together and the electrical code governing the specific installation, none of which this tool can know. The reference figures shown for common gauges are commonly published values, useful for getting in the right ballpark — not a substitute for the actual code or a licensed electrician on anything carrying real power.

Aluminum's resistivity is roughly 1.6× copper's at the same cross-section, which is why aluminum wiring is typically run one or two gauges heavier than copper would need for the same current and voltage drop. This is also why aluminum and copper are never simply substituted gauge-for-gauge in an existing installation without re-checking the sizing.