Consider this. Your car was designed to perform best with up to 20" wheels. Anything more will place stress on suspension, brakes, etc that could end up causing pre-mature failure of those areas. It might look great to the eye, but cold cost you gobs of cash over time. If your car has any remaining warranty left, that will be voided for anything related to the wheel change. I recommend anyone planning on increasing the wheel size over the factory spec to read this article first:
http://money.cnn.com/2004/12/15/pf/auto ... ig_wheels/
Having said that, if you still want to proceed, I recommend this site:
https://www.rimsntires.com/specspro.jsp
It allows you to post the factory specs on the left and your proposed changes on the right. Then it tells you the result of those changes. You can play with offset, tire size and wheel size and see the changes immediately before you buy anything.