The Compass DeRose Guide to American Wire Gauges

This page gives diameter, cross-sectional area, current capacities, weight, and resistance of copper wires in various American Wire Gauge (AWG) sizes.

This page was written by Steven J. DeRose around 2003, and was last updated on 2008-02-21.

Wire diameters are expressed on a numbered scale called "AWG", with larger numbers meaning smaller wire. The scale goes from 40 to 0, then 00, 000, and 0000 (the last one is also sometimes written as "OOOO" or "4/0"). A change of 3 gauge numbers (say, from 15 to 12 gauge) amounts to doubling the cross-sectional area of the wire. Audiophiles will note that this works much the same way as decibels. In this case, each gauge's diameter is about 1.1229322 times the next gauge's.

Current capacity is approximately proportional to cross-sectional area, except for special effects at high frequencies (for larger diameters, the high-frequency effectws kick in at not-so-high frequencies).

The current capacity, weight, and resistance in this table are based on solid copper wire (silver or superconductors will have higher capacity; aluminum less; stranded slightly less). Remember to double weight and resistance for a round-trip circuit. Current capacity also depends on how hot you are willing for the wire to get....

"open air current" is a continuous-duty rating for a single conductor without insulation in open air (not likely in actual practice -- so this is generally just an upper-bound on current capacity). "cable current" applies when the wire is in a multiple conductor cable, and varies with the thermal conductivity of whatever insulation is used, the surrounding air temperature, the number of wires in the bundle, and many other factors. The values for residential power cables (shown in bold) allow an additional safety factor by rounding current capacity down a bit.

A mil is 0.001". A "circular mil" is an odd unit: square a wire's diameter in mils, to get its area in circular mils. Thus, the area number is the same as the cross-sectional area in square mils, of a square shaped wire the same thickness as the circular wire. This will always be larger than the true area of a circular wire, by a factor of π/4.

The current capacities reported by various sources vary, sometimes by quite a bit. This is probably because so many factors are involved, and each site is making slightly different assumptions.

References

See also Wikipedia.

myElectrical Engineering has a nice calculater that lets you pick copper or aluminum wire, the type of insulation, etc., and gives current capacity in a variety of situations. However, you have to look up the wire size by square millimeters. Other pages on the site provide voltage drop information, and an AWG-to-mm2 converter.

Some useful additional information, including metric wire gauges, is here. An interesting but fragmentary discussion of wire ratings is here. He provides a variety of data, some from the Amateur Radio Relay [League] Handbook, 1985, but there seem to be a number of contradictions.

Note: These sources give slightly varying values for nearly every column.

A table very similar to the one above is here. I wish I'd found it before constructing this one. Except, make sure your window is wide enough, since it's not a resizable table.

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