Calculators/ Roofing/Roofing Calculator
Roofing Calculator
Roof area, squares and shingle bundles from the footprint.
A roof is always bigger than the building underneath it. How much bigger depends entirely on the pitch: a 6/12 roof has 11.8% more surface than its footprint, and a 12/12 roof has 41% more. Estimating from floor area alone is the single most common roofing mistake.
How this is calculated
- Add the eave overhang to both dimensions, then multiply for the covered footprint area.
- Apply the pitch multiplier √(1 + (rise÷12)²). For a 6/12 roof that is 1.118, so the roof is 11.8% larger than the footprint.
- Divide by 100 for roofing squares, the unit shingles are sold in. Three bundles of architectural shingles cover one square.
- Add 10% waste for a simple gable, 15% or more for hips, valleys and dormers.
Frequently asked questions
What is a roofing square?
One hundred square feet of roof surface. Shingles are sold by the bundle, with three bundles covering one square for most architectural shingles.
How do I find my roof pitch without climbing up?
Hold a level against a rafter or gable end, mark 12 inches along it, and measure straight down to the roof surface. That drop in inches is the rise.
Does this work for a hip roof?
The total area is the same as a gable of the same footprint and pitch, so the square count holds. Hips need more waste allowance, though, because every course is cut at an angle.