Lenard Zinn suggests propping a bike against a wall, then measuring from the wall to the various points of interest. Then, some arithmetic will yield distances between those points. Heights can be measured from the floor, again with some subtraction or points of interest. All those dimensions will need to be recorded systematically. I use this chart. Road Positioning Chart - Park Tool I continually tweak my fit so that about once a year I measure everything again. I now have 4-5 years of those measurements and find it very interesting to see how my fit has changed in that time with changes in cycling fitness.