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Wire Gauge Converter

Converters · Added

American Wire Gauge runs backwards — a bigger number is a thinner wire — because the scale originally counted how many times the wire had been pulled through a drawing die. Underneath that awkward surface it is a clean geometric series, which is why six gauges down doubles the diameter and three gauges down doubles the cross-section. This converts in both directions, gives the figures in every unit a datasheet or a cable listing might use, and computes the resistance per kilometre for copper or aluminium.

Direction

Changes the resistance figures, not the geometry

How to use the wire gauge converter

  1. 1Choose a direction: a gauge number to metric figures, or a metric cross-section to the nearest gauge.
  2. 2Pick the gauge from the list, or type the area in square millimetres.
  3. 3Choose copper or aluminium — this changes the resistance figures but not the geometry.
  4. 4Press Convert.
  5. 5Use the reference table underneath to compare neighbouring sizes; the row matching your result is highlighted.

Examples

A common household conductor

Input
12 AWG copper
Result
2.053 mm across, 3.309 mm², 5.21 Ω/km

The nearest metric size sold is 2.5 mm², which is slightly thinner — the two scales do not line up neatly anywhere.

Going the other way

Input
2.5 mm²
Result
Nearest is 13 AWG at 2.624 mm²

Metric cable is sold in round cross-sections and AWG in a geometric series, so a match is nearly always approximate.

A thin signal wire

Input
24 AWG copper
Result
0.511 mm across, 0.205 mm², 84.2 Ω/km

Twelve gauges thinner than 12 AWG, which is sixteen times less copper — the scale doubles area every three steps.

About the wire gauge converter

The formula behind the scale

The diameter of gauge n is 0.005 inch times 92 raised to the power of (36 − n) divided by 39. That looks arbitrary until you see what it was chosen to do: fix 36 AWG at 0.005 inch and 0000 AWG at 0.46 inch, and space the thirty-nine steps between them geometrically. The ratio 92^(1/39) is about 1.1229, so each step up in gauge number makes the wire about 12.3% thinner.

Because area goes as the square of diameter, each step changes the cross-section by a factor of about 1.261 — and 1.261 cubed is very nearly two, which is where the three-gauges-doubles-the-area rule comes from. Similarly 1.1229 to the sixth is close to two, giving the six-gauges-doubles-the-diameter rule, and 1.261 to the tenth is close to ten, giving the ten-gauges-times-ten rule. None of these is exact, but all three are accurate to well within the manufacturing tolerance of real wire.

The same geometric structure means the scale extends naturally in both directions. Sizes thinner than 40 AWG exist for fine magnet wire, and the aught sizes extend upward until they are abandoned in favour of kcmil for very large conductors, where a linear area scale is simply more practical.

Where the resistance figures come from

Resistance is resistivity times length divided by cross-sectional area. The resistivity used here is 1.724 × 10⁻⁸ Ω·m for copper and 2.65 × 10⁻⁸ for aluminium, both at 20 °C, which are the standard annealed values that cable specifications are written against. Divide by the area this page computes and you have ohms per metre; multiply by a thousand for the figure usually quoted.

Two caveats apply to any table like this one. Real cable is often stranded rather than solid, and a stranded conductor of the same nominal gauge has slightly more resistance than a solid one — the strands take a helical path and are therefore individually longer than the cable. The effect is a percent or two, small but consistently in the same direction.

The second is temperature. These are 20 °C figures, and copper gains about 0.4% resistance per degree above that. A conductor working near its thermal limit can be 20% more resistive than the table says, which is why the voltage drop calculator on this site asks for a conductor temperature rather than assuming room temperature.

Frequently asked questions

Why do the gauge numbers get bigger as the wire gets thinner?
Because the number records how many times the wire was drawn. Making wire means pulling it through a die that is slightly narrower than the wire, and repeating that with progressively smaller dies. A wire drawn twenty-four times is thinner than one drawn twelve times, so the count and the diameter run in opposite directions. The very thick sizes ran out of numbers below one, which is why 0, 00, 000 and 0000 exist — written 1/0 through 4/0 and pronounced "one aught" to "four aught".
What are the rules of thumb for the scale?
Three of them fall straight out of the definition, and they are worth more than any chart. Six gauges down doubles the diameter. Three gauges down doubles the cross-sectional area, and therefore halves the resistance. Ten gauges down multiplies the area by ten. So 10 AWG has ten times the copper of 20 AWG, and 4 AWG has twice the copper of 7 AWG, without looking anything up.
Why does an AWG size never match a metric size exactly?
Because the two scales were built on different principles. AWG is geometric, with each step a fixed ratio from the last, defined so that 36 AWG is 0.005 inch and 0000 is 0.46 inch with thirty-nine steps between. Metric cable is sold in round cross-sectional areas — 1.5, 2.5, 4, 6, 10 mm² — chosen for convenience rather than by a formula. Nothing forces the two to coincide, and they essentially never do.
What is a circular mil?
The area of a circle one thousandth of an inch in diameter, and it exists to make one calculation easy: the area in circular mils is simply the diameter in mils squared, with no π and no dividing by four. It is still used in North American cable specifications, particularly for large conductors quoted in thousands of circular mils — the MCM or kcmil sizes above 0000 AWG.
Does this tell me what current a wire can carry?
No, deliberately. Resistance follows from the metal and the geometry and is computed here. Current capacity does not: it depends on how hot the insulation is allowed to get, the ambient temperature, whether the cable is bundled with others, and how it is installed. Those are tables in NEC 310.16, IEC 60364-5-52 or whichever code applies where you are, and the same conductor has different ratings under different conditions. A wire has a resistance; a cable in an installation has an ampacity.

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