Roof Pitch Calculator
Convert your roof's pitch (rise per 12″ of run) into true roof surface area, roofing squares, and shingle bundles.
e.g. enter 6 for a “6/12” pitch
How this calculator works
Roof area isn’t the same as your building’s footprint — a sloped roof has more surface area than the flat ground it covers. This calculator applies a pitch multiplier: √(rise² + 12²) ÷ 12, where rise is how many inches the roof climbs per 12 inches of horizontal run (a “6/12 pitch” means 6 inches of rise per 12 inches of run).
Roof area = footprint area × pitch multiplier, then a waste allowance is added for cuts, hips, valleys, and ridges. That total is divided by 100 to get roofing squares (1 square = 100 ft², standard roofing industry unit), and multiplied by bundles-per-square (usually 3 for standard shingles) to get total bundles.
Example calculation
Project: a 40 ft × 30 ft home footprint, 6/12 roof pitch, 10% waste, 3 bundles per square.
- Footprint area = 40 × 30 = 1,200 ft²
- Pitch multiplier = √(6² + 12²) ÷ 12 ≈ 1.118
- Roof area = 1,200 × 1.118 ≈ 1,342 ft²
- With 10% waste ≈ 1,476 ft²
- Roofing squares = 1,476 ÷ 100 ≈ 14.76 squares
- Bundles = 14.76 × 3 ≈ 45 bundles
Buying & material guidance
3-tab shingles typically come 3 bundles per square; architectural/dimensional shingles often run 3–4 bundles per square depending on the manufacturer — always check the product packaging, since coverage varies by brand.
Complex roofs with multiple hips, valleys, and dormers should use a 15% waste allowance instead of the standard 10%, since there are far more angled cuts. Don’t forget underlayment, starter strip, ridge cap shingles, and nails/fasteners — this calculator covers field shingle bundles only.
This tool uses the same calculation engine as our full Roofing Calculator, with guidance tailored to this project type.
Frequently asked questions
How do I measure my roof pitch?+
In the attic, hold a level horizontally against a rafter, mark a point 12 inches out along the level, then measure straight down to the rafter at that mark. That distance in inches is your rise — for example, an 8-inch measurement means an 8/12 pitch.
How many bundles of shingles do I need per square?+
Most standard 3-tab and architectural shingles come 3 bundles to a square (100 ft² of coverage), though some architectural shingle lines use 4 bundles per square — check the specific product's packaging.
How do I calculate roof area from pitch?+
Multiply your building's footprint area by a pitch multiplier of √(rise² + 12²) ÷ 12, where rise is the inches the roof rises per 12 inches of horizontal run. A steeper pitch means a larger multiplier and more roof surface area than the footprint suggests.
What waste percentage should I use for roofing?+
10% is standard for a simple gable roof. Increase to 15% or more for roofs with multiple hips, valleys, dormers, or a steep pitch, since there are more angled cuts and more waste.
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