Wire gauge → mm converter

A wire-gauge number is an ordinal index into a fixed lookup table, not a measurement — higher number = thinner wire (a historical count of drawing passes). Four incompatible tables are in daily use, so one gauge number maps to four different diameters. The tool stores each system’s defining value and converts to mm = inches × 25.4.

AWG (American Wire Gauge) is the only geometric one — d(in) = 0.005×92^((36−n)/39), anchored at #36 = 0.005 in; it governs copper/aluminium conductors (ASTM B258) and must not be used for steel. SWG (Imperial) is a legal fixed-inch table (UK, 1883). BWG/Stubs is the oldest empirical table (tube and hardened wire). US Steel Wire Gauge (Washburn & Moen) is the fixed table US welded mesh, tie wire, nails and fencing are actually quoted in — the tool’s default.

AWG is a constant-ratio geometric series while SWG/BWG/Steel are hand-built legacy tables, so the same number diverges — most at heavy gauges: at 6 gauge the diameter ranges 4.12 mm (AWG) to 5.16 mm (BWG), a 25% spread for the same number.

“16 gauge tie wire”: AWG 1.29 / SWG 1.63 / BWG 1.65 / US Steel 1.59 mm — the last is correct for US tie wire; ordering 16 AWG would give wire ~19% thinner. The reverse lookup returns, per system, the gauge whose stored diameter is nearest the millimetre value entered.

Gauge numbers are dimensionless — always convert to mm on a PO; never cross-reference AWG against the Steel gauge for ferrous wire; the mm value is nominal, as real wire carries a diameter tolerance of roughly ±0.05–0.08 mm.