Harry's Roofing Calculator is a simple calculator developed by the trade, for the trade. Work out rafter lengths on the fly with this handy app. You simply enter the Run, Rise and Spacing, the calculator then gives you Rafter Length, Hip/Valley Rafter length, Plumb Cuts, Seat Cuts and Jack Diminish. A simple tool that does a single job, but it does it well. This is a companion on the work site saving you time, which equates to money.