I have a few books on fit floating around and they say get a general idea of frame size and then take it from there. As the girls have mentioned it can be different from bike to bike. The formula to get a rough idea is listed below.

Get your crotch to floor measurement in centimeters and then multiply this measurement by 0.65 to get frame size.

Remember this is only to get a rough idea at where to start when looking at frame size but I think you will find it comes out with a lot smaller frame than you have mentioned above.

Hope this helps.