I think they have you sit on some sort of gel cushion. The Toupe only comes in 3 sizes, so I am not sure exactly how accurate it is, but it should give you a pretty good idea. The only other thing you may want to consider is that all SMP saddles increase padding with the width as well, and many riders claim to be more comfortable on a stiffer seat. I'm really happy with my 109, seems to be just the right size for me. The padding is still pretty stiff, so my sitbones are not hitting the plastic underneath.