Antenna wire is described using three numbers, the overall size (gauge), the number of strands and the strand thickness. While two wires might be the same gauge, the low frequency performance is not the same if one is a single strand (solid) and the other made up of many fine strands.
Here are the complete description of wires commonly used with RFID. The first number is the gauge, the second the number of strands and the third is the strand size in AWG.
- 22 AWG / 7 / 30 dog fence wire
- 12 AWG / 19 / 24 building construction wire
- 10 AWG / 109 / 30 appliance wire
With low frequency RFID it is important to use the same wire when making a duplicate antenna so the best way to get a proper match is to use the wire with the same number of strands and strand size. This also applies for metric equivalents. There are many conversion tables for AWG and metric sizes but they do not take into account matching these characteristics.