It all depends on what you want the coil to turn out to be?
Do you want a 2.8ohm or 1.8ohm or 3ohm so you can pump 5v thru it?
What Ohm's do you like to vape?
What
device do you vape on?
All of that will lead you to what ohm you want to make, then you just have to use either lower gauge wire 27-28 for a lower ohm or higher for higher Ohm's. Then you have to pick what size wrapping device to use, a 1/16 or 5/64 drill bit or 20g-18g needles, those are what I use most the time.
Its all trial and error, the first few times you may have to re-wrap your coil multiple times to get the right ohms you want, thats a normal process everyone goes through. When all else fails go to Youtube and watch some rebuild videos on protanks, they are all the same but for the protank 3 duel coil. Just follow a video that has about the Ohms that you want, use the same wire and size wrap device and you should hit the mark.
Also buy yourself a good roll of Kanthal, they sell 100ft for like $7 bucks online, it will last you forever, then you dont have to worry about cutting too much or wasting any. When you buy from your local shop $5 per 3ft, you get ripped off for sure.
Good luck, hope something I wrote helps you, keep
vaping!