AWG NEMA / IEC Metric Standard Sizes Chart  Bare Wire Dimensions 
AWG
SIZE
NEMA Nominal Diameter Inches / MM
IEC R20
Series MM
AWG
SIZE
NEMA Nominal Diameter Inches / MM
IEC R20
Series MM
4/0
0.4600
11.684

27
0.0142
0.361
0.355
3/0
0.4096
10.404

28
0.0126
0.320
0.315
2/0
0.3648
9.266

29
0.0113
0.287
0.280
1/0
0.3249
8.252

30
0.0100
0.254
0.250
1
0.2893
7.348

31
0.0089
0.226
0.224
2
0.2576
6.543

32
0.0080
0.203
0.200
3
0.2294
5.827

33
0.0071
0.180
0.180
4
0.2043
5.189
5.000
34
0.0063
0.160
0.160
5
0.1819
4.620
4.500
35
0.0056
0.142
0.140
6
0.1620
4.115
4.000
36
0.0050
0.127
0.125
7
0.1443
3.665
3.550
37
0.0045
0.114
0.112
8
0.1285
3.264
3.150
38
0.0040
0.102
0.100
9
0.1144
2.906
2.800
39
0.0035
0.089
0.090
10
0.1019
2.588
2.500
40
0.0031
0.079
0.080
11
0.0907
2.304
2.240
41
0.0028
0.071
0.071
12
0.0808
2.052
2.000
42
0.0025
0.064
0.063
13
0.0720
1.829
1.800
43
0.0022
0.056
0.056
14
0.0641
1.628
1.600
44
0.0020
0.051
0.050
15
0.0571
1.450
1.400
45
0.00176
0.0447
0.045
16
0.0508
1.290
1.250
46
0.00157
0.0399
0.040
17
0.0453
1.151
1.120
47
0.00140
0.0356
0.035
18
0.0403
1.024
1.000
48
0.00124
0.0315
0.031
19
0.0359
0.912
0.900
49
0.00111
0.0282
0.028
20
0.0320
0.813
0.800
50
0.00099
0.0251
0.025
21
0.0285
0.724
0.710
51
0.00088
0.0224
0.022
22
0.0253
0.643
0.630
52
0.00078
0.0198
0.020
23
0.0226
0.574
0.560
53
0.00070
0.0178
0.0187
24
0.0201
0.511
0.500
54
0.00062
0.0157
0.0157
25
0.0179
0.455
0.450
55
0.00055
0.0140
0.0140
26
0.0159
0.404
0.400
56
0.00049
0.0124
0.0124
AWG
SIZE
NEMA Nominal Diameter Inches / MM
IEC R20
Series MM
AWG
SIZE
NEMA Nominal Diameter Inches / MM
IEC R20
Series MM
Information to be used as a guide only.
AWG (American Wire Gauge)
AWG numbers follow a mathematical formulation devised by Brown and Sharpe in 1855. The AWG designation corresponds to the number of steps by which the wire is drawn. (18 AWG is smaller than 10 AWG, therefore is drawn more times to obtain a smaller cross sectional area.) According to the "Standard Handbook for Electrical Engineers" (Fink and Beaty) 'gauge' is the American Wire Gauge also known as the Brown & Sharpe gauge, which is the standard for which American engineers adhere.
AWG began at 4/0 wire with a diameter of 0.46" and the next lower wire size was derived by multiplying the diameter by 0.890526. These then became tabulated into what we today call the AWG; ranging down to 40 gauge wire at 0.003" in diameter. The primary concern in a mechanical standard is for electrical conductors and current carrying capacity (driven by resistance).
To protect engineers from lawsuits and physical harm a resistance measurement system was implemented to certify that all wire produced in the United States met the DC resistance specifications. The process of measuring the DC resistance is known as the 2terminal method. Click here for Calculations for Litz Wire and AC/DC Resistance.
Although there is a worldwide trend to the International System (SI) or Metric measurement, the current practice in wire measurement in the United States is generally the use of the customary English Units. The current practice of the NAtional Bureau of Standards (NBS), the Institute of Electrical and Electronic Engineers (IEEE), and the The American Society of Testing Materials (ASTM) is to reflect American Wire Gauge in parallel with metric units of measurement.
The American Wire Gauge, like some other gauge systems, does generally represent steps in the wire drawing process. In addition to that, the numbers are retrogressive to the wire size  that is, the larger the number the smaller the wire. These gauge sizes are not arbitrary, but are a geometric progression. With the definition of two sizes in the series of gauge sizes, all size related properties of any gauge in the series is defined by that relationship. With AWG 0000 as 0.4600 inch and AWG 36 as 0.0050 and 38 gauge sizes between these two, the ratio of any diameter to the next larger diameter can be determined as follows:
=
= 1.1229322
The square of this ratio is: 1.2610
This Square of the ratio between sizes can be used as a means of obtaining the resistance, mass and cross section of any wire size if one is memorized these values for only one size. This conversion number can easily remembered as 1 1/4.
Therefore:
Knowing 20 AWG has a crosssection of 1020 circular mils tell us 19 AWG will have 1 1/4 x 1020 or approximately 1250 circular mils. If we had memorized the resistance of 20 AWG as 10 ohms/1000 feet, 19 AWG would have less resistance by 10 ÷ 1 1/4 or approximately 8 ohms/1000 feet.
Since the function os geometric, the cube of this 1 1/4 is approximately 2. This allows you to easily calculate the dimensional functions in 3 gauge increments. Every 3 gauge sizes the resistance, mass per unit, and cross section will double or halve.
Then with a 20 AWG Cross section of 1020 circular mils, 17 AWG will be approximately 2040 mils and 23 AWG will be approximately 510 circular mils.
Using this relationship, with the commitment to memory of the crosssectional area, resistance and mass per unit for any one size, you can quickly move to the value for any other wire size.
For diameter calculation, remembering one diameter, the diameter will double or halve every size gauges and for each gauge the next larger gauge diameter is 120% or 1.2 times the smaller gauge. If you remember six contiguous gauges in mils e.g. 39  44 AWG, you would know all diameters by this rule. Actually, if you just remember 39 AWG as 3.5 mils and the spread between these gauges is 0.3 mil except between 39 and 40 where it is 0.4 mil and 23 and 44 is 0.2 mil, you will have quick access to all gauge diameters.