Custom Military Challenge Coins usually thickness can be 4mm-8mm, if you want better quality, of course the thickness not less than 7mm, if you no need so thick, then the total challenge coins 5-6mm is enough.
For calculating the thickness, some customer check edge thick, some customers use 3D highest thick, it is based on your liking, but as and challenge coins manufacture, we usually calculate the challenge coins thickness based on max. thick, which means we calculate the military challenge coins thickness on the 3D parts.