Seatpost size is a frequent topic here. Almost a year ago I took the time to measure a few posts I have. here's a link to that thread.

Another delay seat post size

BTW the sizing tool (Stein's or other copies) is only the start of proper sizing. It will gage the top of the seat tube, about .5" depth (this for my Odyssey brand size gage). Great to have a sort of first size to trial fit. But seat tube distortion (from either heat and fit up at the time of the frame's being made or too small a post being used previously) is often focused at the bottom of the lug (or where the top tube or seat stays attach). Way too deep for the sizing gage to reach. I've fitted test posts fine at the seat tube's top only to have that post jam when inserted a few inches more. Andy