...many bike fit websites via Google. Depends on leg length mostly/obviously, but other factors too like forward/backward position of the seat. If all fails, go to a LBS and get a quick fit, you may have been off on what was best for you before.

And on a second note, use your rear reflector clamp to locate your seat post height. Put the reflector clamp at the top of your seat tube (in contact). When you pull your seat tube for maintenance/security you will know exactly where it goes when you put it back.