The correct bike size is very important for comfort and health and safety reasons. The table is a guide to help you book the correct size frame.
Size Guide
I see that some people buying bikes hit this page, the above sizes are a guide for renting bikes. The sizes in the table work most times but before you buy go sit on some different sizes and makes. Females should try Giant and Specialized bikes that are made for the female build, not all bike shops stock these so take time to visit a demonstration day before you buy.