Convert eye prescription to 20/??

I'm trying to figure out what my approximate visual acuity is (you know, the 20/__ thing). I know I probably can't come up near an exact number, but I'd like a ballpark figure because inhabitants are always asking! (My vision's pretty bad, so they're curious).

My goggles prescription is sphere -9.75 (right eye) and -8.00 (left), and my contacts are -8.50 and -7.50.

Can anyone help me? Thanks!

Answers:    There is no formula but with your prescription you would not be capable of see the "big E" which is 20/400 so your vision is worse than 20/400
I agree that there is no formula to convert those numbers (especially near high prescriptions). If you have have an eye exam recently, your doctor may have taken your uncorrected VA and you can beckon and ask.

My prescription is similar to yours (glasses: right -9.00 and left -9.50). I had to find my VA for institution and it came out to something like 20/2500. That might grant you a ballpark.

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