How to use this calculator
- Enter or choose units.
- Enter or choose footprint length (with overhangs).
- Enter or choose footprint width (with overhangs).
- Enter or choose pitch given as.
- Enter or choose pitch.
- The roof area updates as you type. Use Copy result or Share to keep it.
Method
Pitch factor = 1 ÷ cos(angle) = √(1 + (rise ÷ 12)²); Roof area = Footprint × Pitch factor; Squares = Roof area (ft²) × (1 + Waste%) ÷ 100; Bundles = Squares × Bundles per square, rounded up
- Footprint
- length × width of the area the roof covers, including overhangs
- rise ÷ 12
- vertical rise per 12 units of horizontal run
- Square
- 100 ft² (9.29 m²) of roof
Worked example
- Footprint = 40 × 30 = 1,200 ft². Pitch factor for 6 in 12 = √(1 + 0.5²) = 1.1180.
- Roof area = 1,200 × 1.1180 = 1,341.6 ft².
- With 10% waste: 1,341.6 × 1.10 ÷ 100 = 14.76 squares; × 3 bundles = 44.3, so order 45 bundles.
A 40 × 30 ft footprint at a 6/12 pitch has about 1,342 ft² of roof, which is 14.76 squares or 45 bundles of shingles with 10% waste.
What the result means
Order whole bundles and keep a few spare for repairs. Ridge caps, starter strips, underlayment and flashing are ordered separately by length.
Assumptions and limits
- All roof planes share the same pitch, so footprint × pitch factor gives the total area for gable and hip roofs alike.
- Roofs with mixed pitches, dormers or curved sections need each section calculated separately.
- Never measure on the roof itself without proper fall protection; footprint measurements from the ground are safer.
Questions
What is a roofing square?
An area of 100 square feet (about 9.29 m²). Shingles and many other roofing products are priced and sold by the square.
How do I find my roof pitch?
Hold a level horizontally against the rafter or roof edge, measure 12 inches along it, then measure straight up to the roof surface. That rise is the pitch in 12.
Please note: Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials.