How it works
Measure the footprint, tell us the pitch, and get the number your supplier quotes in.
Measure the footprint
Length and width of the roof as seen from above, in feet — not along the slope.
Enter the pitch
The rise in inches for every 12 inches of run. A 6/12 roof rises 6 inches per foot.
Get squares and bundles
Roofing is sold by the square. We give you both squares and bundles.
Why the pitch changes everything
Roofing is the one material where the ground measurement is not the answer. A roof seen from above covers a certain footprint, but the actual surface you have to cover is longer, because it slopes. The steeper the roof, the bigger the gap between the two numbers.
The correction is a single multiplier derived from the pitch. Pitch is written as rise over run — a 6/12 roof climbs 6 inches for every 12 inches horizontally. The multiplier is the hypotenuse of that triangle: the square root of 1 plus the rise divided by 12, squared. A 6/12 roof works out to 1.118, so a 1,200 ft² footprint is really 1,342 ft² of shingles. On a 12/12 roof the multiplier is 1.414 — you would be short by more than 40% if you ignored it.
From there, roofing is sold by the square, which is 100 ft² of finished roof, and most three-tab and architectural shingles run 3 bundles to the square. Suppliers deal in whole squares, so round up.
Budget 10% waste on a simple gable roof and closer to 15% on anything with valleys, dormers or hips, since every one of those means cutting shingles at an angle and throwing away the offcut. None of this includes starter strip, ridge cap, underlayment or drip edge, which are ordered separately.
Frequently asked questions
How many bundles of shingles in a square?
Three bundles per square is standard for three-tab and most architectural shingles. Heavier designer shingles can run four or five, so check the wrapper.
How do I find my roof pitch?
Hold a level out 12 inches from the roof surface and measure straight down from the level's end to the roof. That measurement in inches is your rise — a 6 inch drop is a 6/12 pitch.
Does this include ridge cap and starter?
No. Ridge cap, starter strip, underlayment and drip edge are sold separately and calculated by linear foot, not by the square.
How much waste should I add for roofing?
About 10% on a simple gable roof, and 15% when there are valleys, hips or dormers, because those force angled cuts that cannot be reused.
More material calculators
Estimates are for planning only. Confirm quantities with your supplier before ordering.