Shingles are sold in bundles and "squares," and the single biggest estimating mistake is measuring the ground instead of the roof. A roof is bigger than the house under it — sometimes a lot bigger.
Squares and bundles
Roofers count in squares: 1 square = 100 square feet of roof. Standard architectural shingles come 3 bundles to the square, so one bundle covers about 33 square feet. Our shingles calculator turns your roof area into bundles and adds waste.
Measure the slope, not the footprint
The flat outline of your house is smaller than the actual sloped roof surface. If you can safely get on the roof, measure each plane's length × width and add them up. If you measure from the ground, multiply your footprint by a pitch factor:
- Low slope (4/12): about ×1.05
- Medium (6/12): about ×1.12
- Steep (8/12): about ×1.20
- Very steep (12/12): about ×1.41
So a 1,500 sq ft footprint on a 6/12 roof is really about 1,680 sq ft of roof — nearly two extra squares of shingles.
Don't forget the extras
- Starter strip runs along the eaves and rakes — sold separately from field bundles.
- Hip and ridge cap covers the peaks — also separate.
- Waste: add 10% for a simple gable roof, up to 15% for lots of valleys and hips.
- Underlayment: size felt or synthetic to the same roof area with the underlayment calculator.
Order all your shingles from the same production lot so the color matches, and keep a spare bundle for future repairs. Measure carefully, add your waste, and there's no frantic supply run halfway through the tear-off.