AWG Wire Size Calculator

Diameter, cross-sectional area and resistance of any American Wire Gauge size from 4/0 to 40, for copper and aluminium — and the reverse: the AWG size nearest to a metric area in mm².

The AWG formulas (ASTM B258)

AWG sizes, 4/0 to 40

Metric sizes and their AWG neighbours

How the American Wire Gauge works

The American Wire Gauge counts backwards: the bigger the number, the thinner the wire. It comes from wire drawing, where each gauge number was one more pass through a die. ASTM B258 fixes the sizes exactly. 36 AWG is 0.005 inch and 4/0 (0000) is 0.46 inch, with 39 equal ratio steps between them, so each gauge is 92^1/39 ≈ 1.1229 times the diameter of the next thinner one. Two handy consequences follow. Every six gauges the diameter halves, and every three gauges the area, and so the resistance, roughly doubles. 12 AWG is 2.053 mm across and 3.309 mm²; 18 AWG, six gauges thinner, is 1.024 mm.

Resistance. Resistance per length is resistivity divided by area. For annealed copper at 20 °C the international standard (IEC 60028) is 1/58 Ω·mm²/m, or 0.017241; the NIST copper wire tables express the same figure as 10.371 Ω per circular mil-foot. Hard-drawn aluminium, the grade used in conductors, is 0.028264 Ω·mm²/m, about 64% worse. 12 AWG copper measures 5.211 Ω/km, or 1.588 Ω per 1,000 ft. Resistance rises about 0.39% per °C for copper (0.40% for aluminium), so a cable at 70 °C has about a fifth more than the table shows.

Metric sizes. Most of the world sizes conductors by cross-section in mm² (IEC 60228: 1.5, 2.5, 4, 6, 10 mm² and so on). They do not line up with gauges. 2.5 mm² sits between 14 AWG (2.081 mm²) and 13 AWG (2.624 mm²); the second mode of the calculator finds the nearest gauge by area and the smallest gauge that is at least as large, which is the safe direction when substituting one for the other.

Size is not ampacity. This page gives the physical size and resistance of a gauge. How much current it may carry is a different question, answered by your electrical code’s ampacity tables, and depends on insulation temperature rating, installation method, ambient temperature and how many cables are bundled together. The same 12 AWG wire can be rated very differently in a wall, in free air or in a bundle of twenty. To size a cable for a load current and an allowed voltage drop, and to check it against the ampacity from your table, use the wire size calculator; for the voltage and power in a resistance, the Ohm’s law calculator.

Frequently asked questions

Related calculators

References

1. ASTM B258-02. Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors. ASTM International.
2. IEC 60028. International standard of resistance for copper (annealed copper: 1/58 Ω·mm²/m at 20 °C). International Electrotechnical Commission.
3. IEC 60889. Hard-drawn aluminium wire for overhead line conductors (resistivity 0.028264 Ω·mm²/m at 20 °C).
4. National Bureau of Standards. Handbook 100: Copper Wire Tables, 1966 (10.371 Ω·cmil/ft at 20 °C).
5. IEC 60228:2004. Conductors of insulated cables (the metric cross-section series).