I'm using one of the coils it came with. Haven't measured it.
I don't know either, I never even opened the bags. I would assume that they sent big enough coils, so I would suggest using more wick. Personally I build 4mm coils for this thing. The juice/wick holes are 4.5mm diameter so if you use a coil that is too small, you will never have enough wick to fill those holes enough. So a 3.5mm to 4mm is probably preferred for this tank, depending on how tight you want the wick to be. You might could do a 3mm coil if you like really tight wicks in your coils. Anything less than that is probably going to be a bad experience.
EDIT: Just to add with 4mm coils I use about a 10mm wide strip of Japanese cotton to wick it. I will also add that climate, humidity, and probably even altitude may affect how much wicking you need. Basically anything that affects barometric pressure can affect it. This is true for all tanks.