Roofing Calculator
This roofing calculator works out the roof area, the number of roofing squares, and the shingle bundles you need from the plan size and the roof pitch. Enter the dimensions and the roofing calculator returns the sloped area and the materials, so ordering shingles is accurate. It doubles as a shingle calculator and a roof square footage calculator for any pitched roof.
Results
The Roofing Calculator is part of our Materials Estimating collection. Browse more materials estimating to size, convert, and check your work alongside this tool.
What the roofing calculator does
A roof is bigger than its footprint because it slopes, and this roofing calculator accounts for that. It takes the plan area, applies a slope factor from the pitch to get the true sloped area, then converts to roofing squares and shingle bundles. As a shingle calculator it turns the roof square footage into the bundles to order, so figuring shingles no longer means guessing at the pitch.
How the roofing calculator finds the area
The plan area is scaled up by a slope factor that depends on the pitch:
The roofing calculator multiplies the plan area by this factor for the true sloped area, then divides by 100 square feet to get roofing squares, since one square covers 100 sq ft. Shingles come three bundles to the square, so the shingle estimator multiplies squares by three. This is why converting square feet to roofing squares is the heart of figuring shingles.
Roofing calculator example
A roof 10 m by 8 m in plan, at a 6-in-12 pitch, with 10% waste. The slope factor is √(6² + 12²) ÷ 12 = 1.118, so the sloped area is about 89.4 m², or 98.4 m² with waste, roughly 10.6 roofing squares. That needs about 32 shingle bundles. Enter your roof and the roofing calculator returns the squares and bundles.
How to use the roofing calculator
Enter the plan length and width of the roof, then the pitch as a rise over run. The roofing calculator multiplies the plan area by the slope factor for the real sloped area, adds a waste allowance, and returns the roofing squares and shingle bundles. As a roof square footage calculator it also gives the area in square feet, so figuring out roof square footage and converting square feet to roof square is built in, and the roof square estimator rounds up to whole bundles.
Reading the roofing calculator result
The roofing squares figure is how the trade orders and prices shingles: one square is 100 square feet of roof. The bundle count is what you buy, at three bundles per square for standard shingles. Order the waste allowance on top, since hips, valleys, and starter courses cost extra material. The roofing calculator gives the sloped area, not the plan area, which is the number that matters, because a steep roof needs far more shingles than its footprint suggests.
When to use the roofing calculator
- Ordering shingles with the shingle calculator
- Finding roof area with the roof square footage calculator
- Converting area with the square feet to roofing squares calculator
- Estimating bundles with the shingle estimator
- Sizing panels with a metal roof material calculator
Common roofing calculator mistakes
- Using the floor plan area. The roof slopes, so the roofing calculator scales it up by the pitch.
- Forgetting waste. Hips and valleys add cuts; include at least 10% when figuring shingles.
- Ordering by square instead of bundle. Shingles come three bundles per square, which the shingle estimator handles.
Tips for accurate results
- Enter the real pitch so the roofing calculator scales the plan area correctly.
- Add 10% waste for a simple roof, 15% for a complex one.
- Order whole bundles at three per roofing square.
Why pitch drives the roofing calculator
The single thing that separates a roofing calculator from a plain area calculator is pitch. The footprint of a house tells you nothing about how much roof covers it until you know the slope, because a steeper roof stretches more material over the same ground. The slope factor captures this: a gentle 4-in-12 roof adds only about 5% to the plan area, while a steep 12-in-12 roof adds 41%. Ignore the pitch and you will order far too few shingles for a steep roof. This is why figuring shingles always starts by converting the plan area to the true sloped area, which the roofing calculator does from the rise and run you enter.
Roofing squares, bundles, and the shingle calculator
Roofing has its own units, and the roof square footage calculator translates between them. A roofing square is 100 square feet, the standard the trade prices by, and shingles ship three bundles to the square. Waste is the other real-world factor: every hip, valley, ridge, and starter course consumes extra material through cutting and overlap, so a simple gable roof needs about 10% waste while a complex roof with many angles can need 15% or more. The roofing calculator adds your waste allowance before rounding up to whole bundles, because you cannot buy a partial bundle, so the shingle estimator always gives a count you can take straight to the supplier.
Roof square footage calculator slope chart
The slope factor the roofing calculator applies to plan area, by pitch:
| Pitch (rise/12) | Slope factor | Extra area |
|---|---|---|
| 4 / 12 | 1.054 | +5% |
| 6 / 12 | 1.118 | +12% |
| 9 / 12 | 1.250 | +25% |
| 12 / 12 | 1.414 | +41% |
Roofing Calculator FAQ
How do I calculate roofing squares?
Find the sloped roof area in square feet and divide by 100, since one roofing square is 100 sq ft. The roofing calculator does this and also converts square feet to roofing squares for you.
How many shingle bundles per square?
Three bundles cover one roofing square for standard architectural shingles. The shingle estimator multiplies your squares by three and rounds up.
Why is roof area bigger than the floor plan?
Because the roof slopes. The roofing calculator applies a slope factor from the pitch, so a steep roof has far more area, and shingles, than its footprint.
How much waste should I add?
About 10% for a simple roof, more for one with many hips and valleys. The roofing calculator adds your waste allowance before figuring shingles.