Is there a formula for antifreeze

50-50 is the "standard."

You can buy testers, they are essentially a hydrometer just like the age old battery ones, except calibrated for glycol. you can get some pretty cheap ones, the accuracy is in question

be careful buying it. I recently got screwed at the local store. ask the girl for concentrate, and I sure that's what she thought she sold.

only difference i could see is concentrate says so in little letters about 1/8" high on the front. "pre mix" does not go out of the way to tell you