How to calculate roof square footage
Measure the footprint to the roof edge, so the overhangs count, then multiply by the pitch multiplier. A 40 by 30 ft house with 12-inch overhangs is 42 by 32 ft, or 1,344 sq ft in plan. At 6/12 the multiplier is 1.118, which gives about 1,503 sq ft of roof. The same footprint and pitch give the same area whether the roof is a gable or a hip.
When planes have different pitches, measure them separately. Split the roof into rectangles, triangles, and trapezoids, give each its own pitch, and add them up. Include porches, garages, and bump-outs, and subtract any overlap. A plane you measured along the slope doesn't need the multiplier. The roof pitch calculator converts an angle or a level reading if you need the pitch.
Roofing squares, waste, and rounding
A roofing square is 100 sq ft of roof surface, so 1,503 sq ft is 15.03 squares. Waste covers cutting, and there is no standard figure. It runs higher on hips, valleys, and cut-up roofs. Most shingles come three bundles to the square, so orders round up to the next third of a square. The calculator shows the exact squares too.
Checking a measurement report
A measurement report's area is already pitched, so don't multiply it again. Enter it in Report total mode instead. A quick footprint check catches a gross error, such as a missed garage, but expect small differences from mixed pitches, rake overhangs, and dormers.
FAQ
How many squares is a 2,000 sq ft house?
It depends on the footprint and the pitch, not the living area. A one-story house that is 50 by 40 ft, with 12-inch overhangs and a 6/12 roof, is about 24.4 squares before waste. A two-story house with the same living area has about half the footprint.
Why do some charts show 1.732 for a 12/12 roof?
That is the hip and valley factor, which turns a hip's or valley's common run into its length. Roof area at 12/12 uses 1.414.
Can I measure a roof in Google Earth?
You can trace the outline, but that gives the footprint. Add the overhang and apply the pitch multiplier, or use an aerial measurement report.
Frontera's estimating software builds the estimate or supplement from your measurement report, with Xactimate-formatted line items.