Roofing Calculator
ft
ft
Pitch
10%
Total Sq Ft696
Squares6.96
Bundles21
This roofing calculator estimates the surface area of a sloped roof and converts it into roofing squares and the number of shingle bundles to order. It takes the building's footprint length and width, multiplies by a slope factor derived from the roof pitch, and adds a waste allowance. The output gives you total square footage, squares (each 100 sq ft), and bundles at three bundles per square.
Formula
Area = L × W × √(1 + pitch²) × (1 + waste%) ; Squares = Area ÷ 100 ; Bundles = ⌈Squares × 3⌉
- L, W
- Roof footprint length and width in feet
- pitch
- Rise-over-run ratio (e.g. 4/12 = 0.333)
- waste%
- Extra material allowance, expressed as a fraction (e.g. 0.10 for 10%)
- Squares
- Roofing squares, where one square = 100 sq ft
- Bundles
- Shingle bundles, rounded up at 3 bundles per square
How it works
- Enter the roof's footprint length and width in feet (the plan dimensions you would measure from the ground).
- Select the pitch (4/12 through 12/12). The pitch sets the slope multiplier √(1 + pitch²), which stretches the flat footprint into the true sloped area.
- Set the waste percentage with the slider (5-15%). The calculator multiplies footprint area by the slope factor and waste allowance, divides by 100 to get squares, and rounds up to whole bundles at three per square.
Worked example
A 30 ft by 20 ft footprint with a 4/12 pitch and 10% waste.
- Slope factor: √(1 + 0.333²) = √1.111 = 1.0541.
- Area: 30 × 20 × 1.0541 × 1.10 = 695.7 sq ft.
- Squares: 695.7 ÷ 100 = 6.96.
- Bundles: ⌈6.96 × 3⌉ = ⌈20.87⌉ = 21.
About 695.7 sq ft, 6.96 squares, and 21 bundles of shingles.
Frequently asked questions
- What is a roofing square?
- A roofing square is a unit of roof area equal to 100 square feet. Shingles and other roofing materials are usually sold and estimated by the square, with three standard shingle bundles covering one square.
- How does roof pitch affect the material needed?
- A steeper pitch increases the actual sloped surface above the building footprint. The calculator applies the slope factor √(1 + pitch²), so a 12/12 roof needs noticeably more material than a low 4/12 roof on the same footprint.
- Why include a waste percentage?
- Cutting shingles around hips, valleys, ridges, and penetrations creates offcuts, and you want spares for repairs. A 10% allowance is common for simple roofs; complex roofs with many cuts may warrant up to 15%.
- Does this calculator account for hips, valleys, and dormers?
- No. It models a simple sloped plane from the footprint and pitch. For roofs with multiple facets, dormers, or complex geometry, estimate each plane separately or add extra waste to compensate.