Frame size?

My favourite subject, my beater is 54cm, I have a frame in the cupboard that is 55cm, I recently sold a 55.5cm, I am building a 57.5cm and I am about to buy a 59cm. This is called sizing by buying frames, building them up and seeing how well they fit. There is probably a cheaper way.

Sounds familiar. My beater is 56, my Claud Butler is 58 and I've just bought a Peugeot which is a 61. It'll be nice to actually have a bike that fits me.