I don't measure the ratio of epoxy anymore. I use a baby food type jar, squirt about 1/4" of 5 minute or two ton epoxy in the jar right out of the twin tubes(no pre mixing)and slop in enough acetone to fill the jar about half way. I stir this mix with a popsicle stick until I can't see anymore strings of epoxy floating around in the acetone.
You can add more acetone to the mix and get a couple of swipes with your rag during application, but like Pat said, one quick swipe is what you have most of the time.
I have found 5 minute epoxy works OK but doesn't store as long as a solution made from two ton epoxy. I can store the two ton mix for a couple weeks tightly capped before it thickens up.