As your ring starts to form you will need to determine the size you need.This site will convert your ring size to inches or mm.
Tap the ring until you ring size is pretty close. You can be off by a 1-2 mm because there will be extra space in the center to play with.
When you reach about size 6 you can see the date and the words "Liberty", "Quarter Dollar", and "United States Of America" on the inside of the ring. This will be your only proof that you made this from a quarter.