How it works
A sloped roof is bigger than the floor under it. The steeper the roof, the bigger the difference. The pitch multiplier is the number that turns one into the other.
- Footprint = (length + 2 overhangs) × (width + 2 overhangs)
- Pitch multiplier = √(1 + (pitch ÷ 12)²)
- Roof area = footprint × pitch multiplier
- Squares = roof area ÷ 100
Example: a 40 by 30 foot house with 12 inch overhangs has a footprint of 42 × 32 = 1,344 square feet. A 6 in 12 roof has a multiplier of 1.118, so the roof area is 1,344 × 1.118 = 1,503 square feet, or 15.0 squares.
Gable and hip roofs
The formula works for any roof where every surface has the same pitch. A hip roof and a gable roof over the same footprint have the same area. The hip roof just needs more cutting, so it wastes more shingles.
What it leaves out
- Dormers, porches and attached garages. Measure each one as its own rectangle and add the results.
- Sections with a different pitch. Run each section separately.
- Waste. Add 10 to 15 percent when you order. The shingle calculator does that for you.
Common questions
What is a roofing square?
One square is 100 square feet of roof surface. A 1,500 square foot roof is 15 squares. Shingles, underlayment and labor are usually priced by the square.
How do I find my roof area without climbing on the roof?
Measure the length and width of the house at ground level, add the overhang on each side, and multiply that footprint by the pitch multiplier for your roof pitch. This calculator does those steps.
Does a hip roof have more area than a gable roof?
No. Over the same footprint and at the same pitch, both have the same area. A hip roof needs more cuts along the hips, so plan for more waste.
What is the pitch multiplier for a 6/12 roof?
It is 1.118. A 6 in 12 roof has about 11.8 percent more surface than the flat area it covers.
My roof has two different pitches. What should I do?
Split the roof into sections that each have one pitch, run the calculator for each section, and add the areas together.
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