Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of gauge number. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
Gauge numbers are historical and each series is independent: 16 gauge sheet metal is 0.0598 in in the standard steel series but 0.0508 in in galvanised, and wire gauge runs the opposite way with larger numbers meaning thinner wire.
They survive because they are short and familiar, but every gauge number must be converted to an actual dimension before it means anything.
Common misuse
Assuming a gauge number means the same thickness across materials. Steel, galvanised steel, aluminium and stainless all have different gauge tables.