American Wire Gauge chart (4/0–40 AWG)

What each column of the chart means

Diameter (mm, in). The outside width of the bare solid conductor. If you only know a wire's diameter, this is the fastest route back to its gauge: measure the metal, match the number, or let the converter above do it.

Cross-section (mm², kcmil). The amount of copper in a slice of the conductor — the number metric-world engineers size by. 1.5 mm² ≈ 16 AWG, 2.5 mm² ≈ 14 AWG, 4 mm² ≈ 12 AWG, 6 mm² ≈ 10 AWG. Kcmil ("thousand circular mils") is the imperial cousin, and above 4/0 the industry names big wire directly in it.

Resistance (Ω/1000 ft, Ω/km). Copper resistance at 20 °C — the column that answers "will it work at length?", because resistance scales linearly with distance. Count on ~0.4% per °C when the run sits somewhere warm; the copper wire gauge chart shows the ladder in isolation.

Amp rating. A practical current capacity where one exists: NEC Table 310.16 (75 °C column shown here — the dedicated wire gauge amp chart carries all three insulation temperatures for copper and aluminium) for building sizes, automotive free-air values for the thin rows. Insulation rating, bundling, ambient heat and local code all move the real number.

Where the sizes earn their keep

The names in the chart also form a jobs list. On the thick end, 1/0, 3/0 and 4/0 AWG appear in service entrances and feeders. 2 AWG wires inverter leads and grounds; 4 AWG is a 100 A service or RV battery bank. 6 AWG is the 55 A range/oven size and the welder lead. 8 AWG covers the 50 A water heater. Below that sit the household staples — 10 AWG for 30 A dryers and shops, 12 AWG for 20 A receptacles, 14 AWG for 15 A lighting — and then everything flexible and smart-home: 16 AWG speaker and lighting cord, 18 AWG for lamp cord and thermostats, 20 AWG hookup wire, and the craft tiers 26 AWG and 30 AWG where coil winding, jewelry weaving and delicate repair live.

Every one of these rows opens a dedicated page with the nearest metric cable sizes (e.g. "12 AWG → 3.31 mm², next standard conductor is 4 mm²") and the amps for both NEC-style and free-air ratings.

AWG to mm²: honest conversions

Converting between the two systems is where most online charts mislead, because no metric cable is an exact gauge twin. The honest approach is the one used in every row of this chart: compute the exact mm² of the gauge, then name the closest standard metric conductor and say "next larger" — never robot-match. A 12 AWG conductor is 3.31 mm², and the conventional metric pick for the same job is 4 mm²; 14 AWG is 2.08 mm² and its counterpart is 2.5 mm².

The converter above handles three lanes interchangeably: pick an AWG size, type a diameter in mm or inches, or enter an area in mm² or kcmil. It answers with all five numbers plus copper resistance — one reference instead of four mismatched lookup tables.

Copper, aluminium and plating

The chart is calibrated for copper (resistivity 10.371 Ω·cmil/ft at 20 °C). Aluminium conducts roughly 64% worse, so an aluminium conductor needs two gauge steps more copper area than its copper twin for the same job — that's why aluminium service entrances use 2/0 where a copper house entry might use 4/0, and why terminals matter so much. Copper-clad aluminium splits the difference at roughly +10% resistance and 70% of the weight. Tinned copper adds a solderable, corrosion-resistant skin popular in marine and industrial spans; silver plating keeps the skin effect tame at radio frequencies. For the material-by-material view, see the copper chart and the aluminium column of the amp chart.

Print, measure and verify

Two habits make this table trustworthy hands-on. First, when measuring a mystery wire, strip a clean inch and measure the bare metal — jackets lie. Compare your caliper measurement to the diameter column, or hold the conductor against the actual size wire gauge chart, which prints every popular gauge at exactly true scale (verify the 100 mm strip before trusting the printout). Second, remember that stranded bundles measure wider than the solid-diameter column while carrying identical copper; matching by copper area or strand class (see the stranded wire gauge chart) avoids the misread.

How we compute every number

Nothing on this page is transcribed from a supplier brochure. Diameter follows the standard AWG formula d = 0.005 in × 92^((36 − N)/39) for gauge N; area follows from the diameter; copper resistance follows from resistivity 10.371 Ω·cmil/ft at 20 °C; aluminium multiplies that by 1.64. Ampacity rows quote NEC Table 310.16 where the size carries one, and automotive free-air ratings where it does not. That is why the same number always appears on the home chart, the amp chart, the per-gauge pages and in the calculator — one formula, one source of truth, zero mismatched lookups.