Wire Gauge Chart (AWG): Size, Area, Resistance

American Wire Gauge (AWG) sizes solid round wire, and the conductors in most North American electrical cable, by a gauge number: the bigger the number, the thinner the wire. This chart gives every size from 4/0 to 40 AWG with its diameter in inches and millimetres, its cross-section in circular mils and square millimetres, the resistance of copper and aluminium per 1,000 ft, and the weight of bare copper. All of it is computed from the gauge’s defining formula and the international standard for copper’s resistivity, so any row can be checked by hand.

What this chart does not give: ampacity. How many amps a wire may carry in a building is set by the electrical code (NEC Table 310.16 in the US) and depends on the insulation’s temperature rating, the number of conductors together, the ambient temperature and the breaker. Use the code table, the cable’s marking or a licensed electrician, not a generic chart.

AWG wire size chart

How the gauge works

• Every 6 gauge numbers the diameter halves (and roughly every 3 numbers the area halves): 10 AWG is about twice the diameter of 16 AWG.
• Every 10 gauge numbers the area, and the resistance, change by about a factor of 10.
• 36 AWG is defined as 0.005 in and 4/0 as 0.4600 in; the 38 sizes between them form a geometric series, which is where the 92 in the formula comes from (0.4600 ÷ 0.005 = 92).

Using the resistance column: voltage drop

A current flowing through a long cable loses voltage in both the outgoing and the return conductor. For a 15 A load at the end of a 100 ft run of 12 AWG copper, the loop is 200 ft, so the resistance is 0.2 × 1.588 = 0.318 Ω and the drop is 15 × 0.318 = 4.8 V, 4.0% of 120 V. The same run in 10 AWG drops 3.0 V (2.5%). Copper’s resistance rises with temperature, about 0.4% per °C, so a warm cable drops a little more. Many designers aim to keep the drop under a few percent; the code sets the minimum wire size, and a longer run may need a larger one.

Metric sizes: nearest AWG

Wire gauge is not sheet or nail gauge

The AWG formula is the same as the Brown & Sharpe gauge used for aluminium and brass sheet (see the sheet metal gauge chart). Steel wire, fencing wire and the wire of nails and brads use other gauges, so a 16 gauge finish nail is not 16 AWG.

Frequently asked questions

What is the diameter of 12 gauge wire?

0.0808 in (2.05 mm) for solid 12 AWG, with an area of 6,530 circular mils (3.31 mm²).

How many amps can 12 gauge wire carry?

That is set by the electrical code, not by the gauge alone: it depends on the insulation, how the cable is installed and the breaker protecting it. In US homes, look up NEC Table 310.16 and the cable maker’s rating, or ask a licensed electrician.

Is a bigger gauge number a bigger wire?

No, smaller. 10 AWG is thicker than 14 AWG; the “aught” sizes 1/0 to 4/0 are thicker than 1 AWG.

What is 2.5 mm² in AWG?

Between 14 AWG (2.08 mm²) and 13 AWG (2.63 mm²).

What is the resistance of 14 gauge copper wire?

About 2.53 Ω per 1,000 ft at 20 °C.

Sources

1. ASTM B258, Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors: the AWG formula.
2. National Bureau of Standards (now NIST) Handbook 100, Copper Wire Tables, and the International Annealed Copper Standard (IACS): resistivity of annealed copper at 20 °C, 1/58 Ω·mm²/m (10.371 Ω·circular mil/ft), and density 8.89 g/cm³. A US Government work.
3. Aluminium conductor conductivity 61% IACS (typical for EC-grade aluminium, as published by conductor makers).
4. IEC 60228, Conductors of insulated cables: metric conductor size series (names only).

Last reviewed: 24 October 2026. Numbers in the tables are our arithmetic from the sources listed; code sections are summarised, not quoted. How we check our work: methodology and corrections. Spotted an error? Please let us know.