Try this!
The first column is the gauge. Second column is the diameter in mm for that gauge in SWG. Third column is diameter in inches. And finally (because I'm using it myself!) the last column is a diameter in inches which at 1/72nd scale equates to a particular gauge. (So a one-inch diameter in real life is near enough 28-gauge.)
| SWG | SWG | 1/72nd | | dia | dia | scale | gauge | mm | inches | inches | 10 | 3.25 | 0.1280 | 9.22 | 11 | 2.95 | 0.1160 | 8.35 | 12 | 2.64 | 0.1040 | 7.49 | 13 | 2.34 | 0.0920 | 6.62 | 14 | 2.03 | 0.0800 | 5.76 | 15 | 1.83 | 0.0720 | 5.18 | 16 | 1.63 | 0.0640 | 4.61 | 17 | 1.42 | 0.0560 | 4.03 | 18 | 1.22 | 0.0480 | 3.46 | 19 | 1.02 | 0.0400 | 2.88 | 20 | 0.91 | 0.0360 | 2.59 | 21 | 0.81 | 0.0320 | 2.30 | 22 | 0.71 | 0.0280 | 2.02 | 23 | 0.61 | 0.0240 | 1.73 | 24 | 0.56 | 0.0220 | 1.58 | 25 | 0.51 | 0.0200 | 1.44 | 26 | 0.46 | 0.0180 | 1.30 | 27 | 0.42 | 0.0164 | 1.18 | 28 | 0.38 | 0.0148 | 1.07 | 29 | 0.35 | 0.0136 | 0.98 | 30 | 0.31 | 0.0124 | 0.89 | 31 | 0.29 | 0.0116 | 0.84 | 32 | 0.27 | 0.0106 | 0.76 | 33 | 0.25 | 0.0100 | 0.72 | 34 | 0.23 | 0.0092 | 0.66 | 35 | 0.21 | 0.0084 | 0.60 | 36 | 0.19 | 0.0076 | 0.55 | 37 | 0.17 | 0.0068 | 0.49 | 38 | 0.15 | 0.0060 | 0.43 | 39 | 0.13 | 0.0052 | 0.37 | 40 | 0.12 | 0.0048 | 0.35 | Andy