Wire Gauge (AWG) Properties
Pick an AWG size — diameter, area, resistance, and rule-of-thumb ampacity for copper.
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The engineering
AWG is a geometric ladder: 39 steps span a fixed 92:1 diameter ratio between AWG 36 and AWG 0000, so every 6 gauges doubles the diameter, every 3 gauges doubles the area (and halves the resistance), and every 10 gauges is a clean decade of resistance. Once you know one size — AWG 10 ≈ 1 Ω per 100 m — you know them all.
The two ampacity rows are conservative rules of thumb, not code: ~300 circular mils per amp for a single wire in free air (chassis wiring), ~700 cmil/A for wires buried in a bundle or conduit where heat can't escape. Insulation temperature rating, ambient, and (for buildings) the NEC tables override both.
Where this math comes from
Before 1857 every wire mill gauged by its own dies, and 'number 12 wire' meant whatever your supplier said it meant. Joseph R. Brown and Lucian Sharpe's machine-tool firm proposed a mathematically regular series — a pure geometric progression between two anchor diameters — and American industry adopted it as the American Wire Gauge.
The resistance column got its own standard in 1913 when the IEC fixed the International Annealed Copper Standard: 100% IACS conductivity is 1.7241 µΩ·cm, the ρ in this card. Modern electrolytic copper routinely beats it by a percent or two — one of the few specs that improved quietly for a century.
- 1857J. R. Brown & Lucian SharpeBrown & Sharpe gauge — the geometric series adopted as AWG.
- 1913IECInternational Annealed Copper Standard fixes ρ = 1.7241 µΩ·cm.
- 1897National Electrical CodeFirst NEC — wire size becomes a safety regulation, circa.
See the full timeline of the math behind every calculator →
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