How to Measure a Roof

Footprint, Pitch Multiplier, Squares and Waste — From the Ground

Any roof can be measured to within a few percent without leaving the ground, and it takes three steps. First measure the flat footprint: walk the perimeter with a tape or laser measure, record each straight run, add the overhang of twelve to twenty four inches to every outside edge, and break irregular shapes into rectangles and triangles. Second find the pitch, safely, by holding a level against a rafter in the attic or against the gable end, marking twelve inches along it and measuring straight down to the roof line — that drop in inches is your rise over twelve. Third apply the pitch multiplier: 1.0541 at 4:12, 1.1180 at 6:12, 1.2019 at 8:12. The result is true sloped surface, which divided by one hundred gives roofing squares. This guide includes a full worked example, six measuring methods compared on cost and accuracy from ground tape to drone photogrammetry, and the six mistakes that send people back to the supply yard mid-job.