Wire Gauge Chart

American Wire Gauge (AWG) sizes conductors on a logarithmic scale: gauge 36 is fixed at 0.005 in diameter, gauge 0000 (4/0) at 0.46 in, and every step in between follows a constant ratio of 39 steps between those two points. That single geometric rule is what generates every diameter, cross-section and resistance figure in the table below — nothing is looked up from a separate list.

This page gives the full AWG reference at once: diameter in millimetres and inches, cross-sectional area in mm², copper resistance per kilometre, and the closest SWG (British Standard Wire Gauge) equivalent for comparing against non-American cable.

The formula

d(mm) = 0.127 × 92^((36 − n) ÷ 39), where n is the AWG number. Cross-sectional area follows directly from the diameter: A(mm²) = π ÷ 4 × d². A smaller gauge number means a thicker wire — the numbering runs backward from what feels intuitive, because it originally counted how many times a wire had been drawn through progressively narrower dies.

Why the numbers count down as wire gets thicker

AWG traces back to a physical manufacturing process, not an abstract size chart. A wire started as a thick rod and was drawn through a die to thin it, then drawn again through a narrower die, and so on. The gauge number was simply how many passes it had been through — more passes meant a thinner wire and a higher number. Modern wire is not actually made this way anymore, but the numbering stuck.

Reading 1/0 through 4/0

Gauges thicker than 1 AWG are not written as negative numbers on cable — they use the 'aught' notation instead: 1/0 (one-aught), 2/0, 3/0 and 4/0. In the formula above they correspond to n = 0, −1, −2 and −3 respectively. 4/0 is a genuinely substantial conductor, used for heavy service entrance cable and welding leads rather than anything found in a typical household circuit.

Matching AWG to metric cable

American and metric wire are sized on entirely different systems — AWG by a logarithmic gauge number, metric cable directly by cross-sectional area in mm². The mm² column is the bridge between them: a 12 AWG conductor, at roughly 3.31 mm², is close enough to a metric 3.3 mm² or a 4 mm² cable to substitute in most low-voltage work, though always check the actual current rating for the specific insulation and installation method rather than the cross-section alone.

Using this with a voltage-drop calculation

The Ω/km column is the figure a voltage-drop calculation actually needs, since resistance — not gauge number — is what determines the drop across a run of a given length and current. Read the resistance for a candidate gauge, run it through the voltage-drop calculator for the run length and load current, and if the result exceeds about 3% on a branch circuit, move up to the next thicker gauge and check again.