This is a pretty convenient way to add sliding shelves to an existing cabinet. No measuring is needed. Just pry out the old shelf, put this already assembled unit inside the cabinet, remove the shelves, screw the frame to the bottom of the cabinet with the included wood screws, and put the shelves back in. A local company charges a LOT more to put sliding shelves in a cabinet than this cost, and I'm sure that the results are no better.