ElectricalCharts

Wire Gauge Chart

Every AWG and kcmil size with diameter, area, resistance and estimated amp capacity, computed from the ASTM B258 gauge formula.

Quick answer

AWG diameter follows d = 0.005 × 92^((36 − n) / 39) inches. Smaller gauge numbers are thicker wire: one step is about 12.2% more diameter and 26% more area, three steps roughly double the area. Above 1 AWG the sizes run 1/0 to 4/0, then switch to kcmil.

AWG and kcmil gauge chart

Diameter is the bare conductor. Resistance is DC at 75 °C. Amps is the estimated 75 °C copper ampacity at 30 °C ambient.

SizeDiameter (in)Diameter (mm)Circular milsArea (mm²)Ω / 1000 ft (Cu)Est. amps (Cu 75 °C)THHN OD (in)
18 AWG0.04031.0241,6240.826.386110 A0.084
16 AWG0.05081.2902,5831.314.015113 A0.096
14 AWG0.06411.6284,1072.082.525218 A0.111
12 AWG0.08082.0526,5303.311.588224 A0.130
10 AWG0.10192.58810,3835.260.998832 A0.164
8 AWG0.12853.26416,5108.370.628244 A0.216
6 AWG0.16204.11526,25113.300.395159 A0.254
4 AWG0.20435.18941,74121.150.248580 A0.324
3 AWG0.22945.82752,63526.670.197093 A0.352
2 AWG0.25766.54366,37133.620.1563108 A0.384
1 AWG0.28937.34883,69342.410.1239126 A0.446
1/0 AWG0.32498.252105,53553.490.0983146 A0.486
2/0 AWG0.36489.266133,07767.430.0779170 A0.532
3/0 AWG0.409610.404167,80685.010.0618198 A0.581
4/0 AWG0.460011.684211,600107.220.0490230 A0.642
250 kcmil0.500012.700250,000126.680.0415257 A0.711
300 kcmil0.547713.912300,000152.000.0346289 A0.766
350 kcmil0.591615.027350,000177.340.0296319 A0.817
400 kcmil0.632516.065400,000202.710.0259348 A0.864
500 kcmil0.707117.960500,000253.350.0207403 A0.949
600 kcmil0.774619.675600,000304.030.0173454 A1.051
750 kcmil0.866021.996750,000380.010.0138524 A1.158
Computed values — no code table is reproduced. Insulated OD is a nominal THHN/THWN-2 dimension used for conduit fill.
Published standard — source: ASTM B258 AWG geometric series; resistivity 10.371 Ω·cmil/ft for copper

Source & method: Diameter, circular mils and resistance are exact computed values. Ampacity is modelled — see the methodology page.

Gauge step relationships

ChangeDiameterArea / circular milsResistance
1 gauge smaller number×1.123×1.261×0.793
3 gauges smaller number×1.416×2.005×0.499
6 gauges smaller number×2.005×4.020×0.249
10 gauges smaller number×3.249×10.556×0.095

These ratios are why "go up two sizes for a long run" is such a common rule of thumb: two steps cut resistance by roughly 37%, which cuts voltage drop by the same proportion. Check it on a real run.

Frequently asked

How is AWG wire gauge defined?
AWG is a geometric series. 36 AWG is 0.005 inches and 4/0 AWG is 0.46 inches, with 39 steps between them. Each step multiplies the diameter by the 39th root of 92, about 1.1229, so the diameter formula is 0.005 × 92^((36 − n) / 39) inches.
Does a bigger AWG number mean a bigger wire?
No, it is the opposite. Smaller AWG numbers are larger conductors. 10 AWG is thicker than 14 AWG. Above 1 AWG the sizes continue as 1/0, 2/0, 3/0 and 4/0, then switch to kcmil.
How much does wire diameter change per gauge step?
One gauge step changes the diameter by about 12.2% and the cross-sectional area by about 26%. Three gauge steps roughly double the area, and six steps roughly double the diameter.
What is a circular mil?
A circular mil is the area of a circle one mil (0.001 inch) in diameter. Circular mils equal the diameter in mils squared, which makes area comparisons between gauges simple arithmetic.
What does kcmil mean?
kcmil is thousands of circular mils, used for conductors larger than 4/0 AWG. A 250 kcmil conductor has 250,000 circular mils of cross-section, about 19% more than 4/0.

Gear for sizing and pulling wire

Gear for sizing and pulling wire

Tools that pair with the sizes in this chart.

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