How to use the awg wire gauge converter
- Choose what you know: an AWG gauge number, a diameter in millimeters or inches, or a cross-section area in square millimeters.
- Enter the value. For gauge numbers, 0 is 1/0, -1 is 2/0, -2 is 3/0 and -3 is 4/0.
- Read the matching diameter, area, circular mils and resistance per kilometer and per 1,000 feet. When you started from a measured size, the tool names the nearest standard gauge.
- Use the table of neighboring sizes to compare the next sizes up and down.
Formula
diameter in mm = 0.127 x 92^((36 - n) / 39)
gauge n = 36 - 39 x ln(d / 0.127) / ln(92)
area = pi x d^2 / 4
resistance per km = resistivity x 1000 / area
circular mils = (diameter in thousandths of an inch)^2
Resistivity is in ohm square millimeters per meter. The example value, 0.017241, is for copper near 20 degrees Celsius. Aluminum is roughly 0.0282.
Common sizes
12 AWG has a diameter of 0.127 x 92^(24 / 39) = 2.0525 mm (0.0808 inch) and an area of 3.3088 mm2, or 6.53 kcmil. With the copper example resistivity, that is 5.211 ohms per kilometer, or 1.588 ohms per 1,000 feet. 30 AWG is 0.2546 mm across and 338.5 ohms per kilometer.
A wire measured at 1.00 mm across falls at gauge 18.20, so the nearest standard size is 18 AWG. A cross-section of 2.5 mm2 comes out at gauge 13.21, near 13 AWG, and the next size with a slightly larger area is 12 AWG. 4/0 is 11.684 mm across, with an area of 107.2 mm2.
How the gauge scale works
The scale runs backward: a bigger gauge number means a thinner wire. Each step of one gauge changes the diameter by the same ratio, about 12 percent, so every 6 gauges halves the diameter and every 3 gauges halves the area. Sizes larger than 0 are written with a slash, such as 2/0, and counted back through 000 and 0000.
What this tool does not decide
It tells you the size and resistance of solid round wire. It does not say how much current the wire may safely carry, which depends on the insulation, the bundling, the temperature and the rules of your location. Stranded wire has a slightly larger overall diameter than solid wire of the same area. To see how much voltage a wire run loses, use the Wire Voltage Drop Calculator.
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Assumptions and limits
- The wire is solid, round and made of one metal.
- The gauge follows the standard geometric formula between 4/0 and the smallest sizes.
- The resistance is for a straight wire at the temperature of the resistivity you entered.
- Stranded wire, insulation and plating are not modeled.
- The resistivity and the sizes in the form are examples. Use the data for your wire.
Frequently asked questions
Why do gauge numbers get smaller as wire gets thicker?
The scale comes from the old process of drawing wire through a series of dies. Each draw made the wire thinner, so a wire pulled through more dies had a higher gauge number.
How do I convert mm2 to AWG?
Find the diameter from the area with d = sqrt(4 x area / pi), then use the gauge formula. The tool does this when you choose area as the starting point, and names the closest standard size.
Does a bigger number mean more resistance?
Yes. A higher gauge number is a thinner wire, which has less area and more resistance per unit length. Every 3 gauges roughly doubles the resistance.
What is a circular mil?
It is a unit of area equal to the area of a circle one thousandth of an inch (one mil) across. The area of a round wire in circular mils is its diameter in mils squared, and kcmil means thousands of circular mils.