How to convert eye prescriptions from one format to another?

Question

I recently got a new prescription. I was wondering how I convert it from the way the doctor wrote it to the 20/? format which I can understand easier. I forget what the exact numbers were, but I think they were -3.00 and -3.25 or -3.25 and -3.50. Is there a formula that I could use, or could someone tell me approximate numbers?

Answer 1

20/100 or  -1.50

20/200 or  -2.50

20/300 or  -3.00

20/400 or  -4.00

20/550 or  -5.00

20/770 or  -6.00

Answer 2

They can't be converted.  Acuity needs to be measured, your eye doctor would have measured it, so if you want to know call and ask.

The table provided by the first answer is a very rough guide and may or may not apply to you.