AWG Wire Gauge Chart

How to use the AWG chart and calculator

Type a gauge in AWG to size to get its diameter, cross-section area and resistance, with the formulas worked through for that gauge; the matching row in the chart is highlighted. Sizes above 1 AWG can be typed as 1/0 to 4/0 or as 0 to 0000. To go the other way, type a metric conductor size in mm² to nearest AWG: you get the gauge closest on the AWG scale and the smallest gauge that is at least as large. The page address keeps both inputs, so you can bookmark or share a lookup.

The AWG formula

American Wire Gauge is defined by two fixed points — 36 AWG is exactly 0.005 in (0.127 mm) and 4/0 is exactly 0.46 in — with 39 equal ratio steps between them (4/0 counts as n = −3, so 36 − (−3) = 39). That gives:

d(mm) = 0.127 × 92^((36 − n) ÷ 39) A = π ÷ 4 × d² R = ρ ÷ A, with ρ = 1/58 Ω·mm²/m = 0.0172414 Ω·mm²/m

The resistivity is the International Annealed Copper Standard (100% IACS) value at 20 °C, the reference used by the NIST copper wire tables. Area in circular mils is simply the diameter in thousandths of an inch, squared; a kcmil is 1,000 circular mils. Every value in the chart is calculated from these formulas rather than copied from a printed table, and agrees with the published NIST values to within rounding.

Three rules of thumb fall out of the ratio of 92^(1/39) ≈ 1.123 per gauge:

• 6 gauges smaller halves the diameter (92^(6/39) ≈ 2.005): 10 AWG is 2.588 mm, 16 AWG is 1.291 mm.
• 3 gauges smaller halves the area and doubles the resistance: 10 AWG is 3.277 Ω/km, 13 AWG is 6.571 Ω/km.
• 10 gauges smaller is about one-tenth of the area: 1/0 AWG is 53.48 mm², 10 AWG is 5.261 mm².

Worked example: 12 AWG

1. Diameter: d = 0.127 mm × 92^((36 − 12) ÷ 39) = 0.127 × 92^0.61538 = 0.127 × 16.162 = 2.0525 mm (0.080808 in, or 80.808 mil).
2. Area: A = π ÷ 4 × 2.0525² = 3.3088 mm², or 80.808² = 6,529.9 circular mils = 6.5299 kcmil.
3. Resistance: R = 0.0172414 ÷ 3.3088 = 0.0052108 Ω/m = 5.2108 Ω/km, and 5.2108 × 0.3048 = 1.5883 Ω per 1,000 ft.

That resistance is what you need for a voltage-drop estimate. A 20 m cable run has 40 m of conductor (out and back), so R = 0.04 km × 5.2108 Ω/km = 0.20843 Ω. At 10 A, Ohm’s law gives a drop of 10 × 0.20843 = 2.0843 V — try other currents in the Ohm’s law calculator. Real cable runs warmer than 20 °C, which raises the resistance (see below).

Metric sizes and their nearest AWG

Most of the world sizes conductors by cross-section in mm², using the standard series in IEC 60228. The two systems don’t line up, so “equivalent” gauges are approximations. Calculated with the tool above:

IEC 60228 conductors are specified mainly by their maximum resistance rather than an exact geometry, so a real “2.5 mm²” conductor may contain slightly less copper than its name suggests. Treat this table as a guide to physical size, not as permission to substitute one cable for another.

Why there are no ampacity numbers here

Many wire charts print a single “max amps” figure next to each gauge. We don’t, because no single figure is correct. The current a cable may carry depends on the insulation’s temperature rating (for example 60 °C, 75 °C or 90 °C), the installation method (in conduit, in a wall with thermal insulation, clipped direct, buried or in free air), the ambient temperature, how many current-carrying conductors are grouped together, the rating of the terminals, and the voltage drop you can accept over the length of the run. Each wiring code turns those factors into its own tables and corrections: the NEC (NFPA 70) in the United States, IEC 60364-5-52 internationally, and national versions such as BS 7671 in the UK. Use the one that applies where you live, and have mains work done or checked by a licensed electrician.

Limits of the chart

• Temperature. Copper’s resistance rises by about 0.393% per °C near room temperature (the IACS coefficient, 0.00393 per °C at 20 °C). At 60 °C a conductor’s resistance is roughly 16% higher than the chart value.
• Stranded wire. Stranded conductors of the same gauge have slightly higher resistance per unit length, because the strands spiral and are a little longer than the cable.
• Other metals. Aluminum conductors have about 61% of copper’s conductivity, so their resistance is about 1.64 times the copper figure for the same gauge.

For converting the diameters, see millimeters to inches; for the running cost of the equipment on the end of the cable, the electricity cost calculator. More tools are in the electricity section.