The way I actually fit myself, is I draw out various frames I am familiar with, frames I own, and I have CAD for those frames. Then when I am interested in a design, I look at the numbers, and I scale a picture of the frame in CAD from knowns like rim size, or I take a test ride and jot down real numbers.

While I make frames this is all basic stuff anyone could do in sketch-up I suppose, or on brown paper.

Over time as your files increase, as your experience riding and fitting yourself increases, you have some real numbers to deal with. I always wonder about people who show up asking to be fit, many people have owned a dozen or more bikes by that time, yet every bike they approach like a blank slate.