GUIDE

Copper Wire Gauge Chart

All-copper reference: exact diameters in mm and inches, areas in mm² and kcmil, and resistance per 1000 ft and km — computed straight from the AWG formula and copper's known resistivity.

Solid annealed copper (20 °C)

Ω/1000 ft and Ω/km; amps column is NEC 75 °C where the size is rated.

AWG	Diameter (mm)	Diameter (in)	Area (mm²)	Cu Ω/1000 ft	Cu Ω/km	Typical amps
4/0	11.68	0.460	107.22	0.049	0.16	230
3/0	10.40	0.410	85.03	0.062	0.20	200
2/0	9.27	0.365	67.43	0.078	0.26	175
1/0	8.25	0.325	53.48	0.098	0.32	150
2	6.54	0.258	33.63	0.156	0.51	115
4	5.19	0.204	21.15	0.248	0.82	85
6	4.12	0.162	13.30	0.395	1.30	65
8	3.26	0.128	8.37	0.628	2.06	50
10	2.59	0.102	5.26	0.999	3.28	35
12	2.05	0.081	3.31	1.588	5.21	25
14	1.63	0.064	2.08	2.525	8.29	20
16	1.29	0.051	1.31	4.015	13.17	18
18	1.02	0.040	0.82	6.385	20.95	14
20	0.81	0.032	0.52	10.152	33.31	30
22	0.64	0.025	0.33	16.143	52.96	21

Everything here is copper, calculated from first principles

Every diameter, area and resistance in this chart is derived from the AWG formula and copper's 20 °C resistivity of 10.371 Ω·cmil/ft. Widths like "12 AWG = 1.588 Ω/1000 ft" come from R = ρ·L/A and apply to any solid annealed copper wire of that size, from any mill.

Reading the resistance column against length

Resistance markets itself in per-foot terms, but circuits care about the whole run: 50 ft of 12 AWG is 0.079 Ω round-trip, which at 20 A drops 3.2 V — fine on a dryer circuit at 240 V, fatal at 12 V. The ohmKm column exists for metric-plan engines and marine systems.

Temperature extension

Copper's resistivity climbs ~0.4% per °C. A 75 °C-rated conductor at full load is warmer than the table number that sized it; design with that margin already accounted for (the ampacity table embeds it) and don't double-derate unless you're doing something unusual.

Copper wire gauge chart: reading resistance like a ruler

Resistance is the property that decides distance, and the copper ladder reads cleanly: every 10 gauge steps multiply Ω/1000 ft by roughly six, every step roughly ×1.26. 14 AWG answers 2.53 Ω, 12 AWG 1.59 Ω, 10 AWG 0.999 Ω, 8 AWG 0.628 Ω, 4 AWG 0.249 Ω, 2 AWG 0.156 Ω per 1000 ft at 20 °C. Voltage drop is that number times the round-trip length in thousands of feet times the amps. Temperature adds ~0.4% per °C, so a 60 °C engine bay runs about 15% more resistive than the chart — worth counting in vehicle work, forgotten in most attic jobs.

Purity, plating and the aluminium question

Pure ETP copper ("electrolytic tough pitch", 99.9%+) is the baseline conductor for every column above. Gold and silver plating change corrosion, not ohms — a fact that saves money when buying connectors. Untinned copper dulls green in damp air; the skin win is thinner than it looks, so tinning is a marine requirement and optional elsewhere. Aluminium at the same AWG carries ~64% more resistance, so a rating two sizes thicker is the equivalence rule of thumb; CCA (copper-clad aluminium) splits the difference at roughly +10% resistance and deserves its "+2 sizes" caution in any critical circuit.

Solid vs stranded for flex and terminals

Construction decides where the copper lives its life. Solid wire seats perfectly under screw terminals, resists cold creep, and is the right copper for residence branch circuits — but fatigue-cracks after a few sharp bends. Stranded copper survives vibration and motion for decades (see the stranded wire gauge chart for strand classes), which is why vehicles, appliances and test leads use it; its termination trade is ferrules or soldered ends wherever a screw clamp lands. Fine-drawn copper also grades by temper: dead-soft spools for jewelry and craft coiling that the jewelry wire gauge chart picks by hardness — same metal, different bending rules.

Frequently asked questions

Why is copper the standard conductor?

Copper pairs low resistivity (1.68 × 10⁻⁸ Ω·m) with easy joining, corrosion resistance and ductility. Only silver conducts better; aluminium is cheaper but needs bigger cross-sections and special connectors.

What is the resistance of 12 AWG copper wire?

1.588 Ω per 1000 ft at 20 °C (5.21 Ω/km). Resistance rises with temperature roughly +0.4% per °C, so a hot 50 °C run reads about 12% higher.

How much does copper wire weigh?

Multiply 8.96 g/mm² per metre by the cross-section: 12 AWG (3.31 mm²) weighs 29.7 g per metre. That number is why aluminium feeders dominate long runs.

Does copper resistivity change with temperature?

Yes — about 0.0039 per °C. Tables are quoted at 20 °C; hot engine-bay wire can be 10–15% more resistive, which slightly worsens voltage drop.

What gauge is 4 mm² copper wire?

4 mm² sits between 12 AWG (3.31 mm²) and 11 AWG (4.17 mm²): metric lists it as the close cousin of 12 AWG, and jobs sized for 4 mm² comfortably accept 12 AWG and its 20 A household rating.