Roofing Calculator
How many bundles of shingles for that roof?
How this is calculated
- Footprint = length × width
- Pitch multiplier = √(rise² + 12²) ÷ 12 — the hypotenuse factor of the slope
- Roof area = footprint × multiplier
- Squares = roof area ÷ 100; bundles = squares × 3 (3 bundles cover one square)
Common questions
How many bundles of shingles do I need?
Three bundles cover one roofing square (100 sq ft) for standard 3-tab shingles. A 30 × 40 house with a 6/12 pitch has a 1,342 sq ft roof — about 13.4 squares, so 41 bundles round to 42. Architectural shingles are thicker; check the label, some run 4 bundles per square.
What is a square in roofing?
One square = 100 sq ft of roof area. Roofers quote, and suppliers price, by the square. A typical US home is 15-25 squares, and the roof surface is always bigger than the house footprint because of the slope.
How does roof pitch affect the amount of shingles?
Pitch lengthens the surface: a 6/12 pitch multiplies the footprint by 1.118, an 8/12 by 1.202, and a 12/12 by 1.414. A steep roof needs up to 41% more shingles than flat-plan area suggests — the pitch multiplier in the results shows your exact factor.
How do I measure my roof pitch?
From the attic or a rafter: hold a level horizontally, mark 12 in from one end, and measure straight down from that mark to the rafter. That vertical distance in inches is the "rise" — 6 inches down means 6/12 pitch. Or count: most modern suburban homes are 4/12 to 6/12.
What else do I need besides shingles?
Underlayment (1 roll per square roughly), drip edge, ridge cap (buy pre-cut ridge shingles or cut your own — one bundle per 35 lin ft), starter strips, and nails (about 320 per square, usually coil nails for a gun). Add 10-15% for valleys, hips, and starter courses on complex roofs.