If you're in London, go into Rigby and Peller. As far as I know, they'll measure you for free and if they're good enough for the Queen then they're good enough for me!
Posted by Ragingwitch
My daughter went to them, and they are also a place that does it by sight. Their bras are expensive, but if you can afford it, they are excellent,and worth it, particularly if you are a large cup size.