Hi There Sheena. For both you can use say a Scale 1/2" which'd be 0.020" which for BARE wire would be AWG 25 but if you were to wander up or down a bit, no problem. Now the whole thing gets turned over when Insulation to the equation. Say you want a Red + Battery Cable and a Black -. Then you, given the degree that you want to be accurate (keeping in mind - The If your Eye Likes it and it's Your Build, it's OK Rule) may want to get a Micrometer and check for overall thickness. Now for bare wire here's a conversion chart that you can convert Inchs to Wire Gages, AWG for the US. http://www.csgnetwork.com/wireconversiontable.html