Wire Gauge and Current Limits

AWG Wire Sizes (see table below)

AWG: In the American Wire Gauge (AWG), diameters can be calculated by applying the formula D(AWG)=.005·92((36-AWG)/39) inch. For the 00, 000, 0000 etc. gauges you use -1, -2, -3, which makes more sense that "double nought." This means that in American wire gage every 6 gauge decrease gives a doubling of the wire diameter area, and every 3 gauge decrease doubles the wire cross sectional area. Just like dB in signal levels. (Thanks to Paul D. for setting this straight).

Metric Wire Gauges (see table below)
Metric Gauge: In the Metric Gauge scale, the gauge is 10 times the diameter in millimeters, so a 50 gauge metric wire would be 5 mm in diameter. Note that in AWG the diameter goes up as the gauge goes down metric is the opposite. Probably because of this confusion, most of the time metric sized wire is specified in millimeters rather than metric gauges.

Load Carrying Capacities (see table below)
The following chart is a guideline of ampacity or copper wire current carrying capacity following the Handbook of Electronic Tables and Formulas for American Wire Gauge. As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility.
 AWG gauge Diameter Inches Diameter mm Ohms per 1000 ft Ohms per km Maximum amps for chassis wiring Maximum amps for power transmission OOOO 0.46 11.684 0.049 0.16072 380 302 OOO 0.4096 10.40384 0.0618 0.202704 328 239 OO 0.3648 9.26592 0.0779 0.255512 283 190 0 0.3249 8.25246 0.0983 0.322424 245 150 1 0.2893 7.34822 0.1239 0.406392 211 119 2 0.2576 6.54304 0.1563 0.512664 181 94 3 0.2294 5.82676 0.197 0.64616 158 75 4 0.2043 5.18922 0.2485 0.81508 135 60 5 0.1819 4.62026 0.3133 1.027624 118 47 6 0.162 4.1148 0.3951 1.295928 101 37 7 0.1443 3.66522 0.4982 1.634096 89 30 8 0.1285 3.2639 0.6282 2.060496 73 24 9 0.1144 2.90576 0.7921 2.598088 64 19 10 0.1019 2.58826 0.9989 3.276392 55 15 11 0.0907 2.30378 1.26 4.1328 47 12 12 0.0808 2.05232 1.588 5.20864 41 9.3 13 0.072 1.8288 2.003 6.56984 35 7.4 14 0.0641 1.62814 2.525 8.282 32 5.9 15 0.0571 1.45034 3.184 10.44352 28 4.7 16 0.0508 1.29032 4.016 13.17248 22 3.7 17 0.0453 1.15062 5.064 16.60992 19 2.9 18 0.0403 1.02362 6.385 20.9428 16 2.3 AWG gauge Diameter Inches Diameter mm Ohms per 1000 ft Ohms per km Maximum amps for chassis wiring Maximum amps for power transmission 19 0.0359 0.91186 8.051 26.40728 14 1.8 20 0.032 0.8128 10.15 33.292 11 1.5 21 0.0285 0.7239 12.8 41.984 9 1.2 22 0.0254 0.64516 16.14 52.9392 7 0.92 23 0.0226 0.57404 20.36 66.7808 4.7 0.729 24 0.0201 0.51054 25.67 84.1976 3.5 0.577 25 0.0179 0.45466 32.37 106.1736 2.7 0.457 26 0.0159 0.40386 40.81 133.8568 2.2 0.361 27 0.0142 0.36068 51.47 168.8216 1.7 0.288 28 0.0126 0.32004 64.9 212.872 1.4 0.226 29 0.0113 0.28702 81.83 268.4024 1.2 0.182 30 0.01 0.254 103.2 338.496 0.86 0.142 31 0.0089 0.22606 130.1 426.728 0.7 0.113 32 0.008 0.2032 164.1 538.248 0.53 0.091 Metric 2.0 0.00787 0.200 169.39 555.61 0.51 0.088 33 0.0071 0.18034 206.9 678.632 0.43 0.072 Metric 1.8 0.00709 0.180 207.5 680.55 0.43 0.072 34 0.0063 0.16002 260.9 855.752 0.33 0.056 Metric 1.6 0.0063 0.16002 260.9 855.752 0.33 0.056 35 0.0056 0.14224 329 1079.12 0.27 0.044 Metric 1.4 .00551 .140 339 1114 0.26 0.043 36 0.005 0.127 414.8 1360 0.21 0.035 Metric 1.25 .00492 0.125 428.2 1404 0.20 0.034 37 0.0045 0.1143 523.1 1715 0.17 0.0289 Metric 1.12 .00441 0.112 533.8 1750 0.163 0.0277 38 0.004 0.1016 659.6 2163 0.13 0.0228 Metric 1 .00394 0.1000 670.2 2198 0.126 0.0225 39 0.0035 0.0889 831.8 2728 0.11 0.0175 40 0.0031 0.07874 1049 3440 0.09 0.0137