Roofing Calculator
Enter the footprint of the house and the roof pitch. The calculator gives the roof area in square feet and square meters, the number of roofing squares, and how many bundles to buy at the bundles per square printed on your shingle packaging.
Added to all four sides of the footprint. Leave empty or at 0 for none.
6 means a 6/12 roof. Enter 0 for a flat roof.
Your own allowance for cuts. 0 for none.
Check your product's packaging. It varies by shingle.
Roof area (sq ft)
1,502.64
Roof area (m²)
139.6
Roofing squares
15.0264
Squares with 10% waste
16.529
Bundles to buy
50
Footprint (sq ft)
1,344
Pitch factor
1.11803
Roof angle
26.6°
Pitch factor = √(1 + (rise ÷ 12)²), and roof area = footprint × pitch factor. One roofing square is 100 sq ft. Bundles are rounded up to a whole bundle. Areas, squares and the pitch factor are rounded to six significant figures, the angle to 0.1°.
How to use the Roofing Calculator
- Choose how to enter the footprint. "Length and width" is for a rectangle and lets you add an overhang. "Footprint area" takes a total you already have, such as one from a plan.
- Pick feet or meters. With feet the overhang is in inches, with meters it is in centimeters.
- Enter the pitch as the rise per 12 of run. A 6/12 roof is 6, and a flat roof is 0.
- Type your waste percentage and the bundles per square from your shingle packaging.
- Read the roof area, the squares with and without waste, and the bundles. The results update as you type, so there is no button to press.
The roof area formula
Pitch factor = √(1 + (rise ÷ 12)²) Roof area = footprint × pitch factor Squares = roof area in sq ft ÷ 100 Bundles = squares × (1 + waste % ÷ 100) × bundles per square, rounded up
A sloped roof has more surface than the ground it covers. For every 12 of run, the roof climbs by the rise, so the slope is √(12² + rise²) long. Divide that by 12 and you get the pitch factor. With "Length and width", the overhang goes on all four sides first, so a 40 × 30 ft house with a 12 in overhang has a 42 × 32 ft footprint. The formula assumes every roof plane has the same pitch. For sections at different pitches, run each one on its own and add the results. The calculator keeps every figure exact until the end, rounds areas, squares and the pitch factor to six significant figures, and rounds bundles up to a whole bundle.
Worked example
The fields start with these numbers, so you can check each result. A house 40 ft by 30 ft with a 12 in overhang has a footprint of 42 × 32 = 1,344 sq ft. A 6/12 pitch gives a pitch factor of √(1 + 0.5²) = √1.25, shown as 1.11803, and a roof angle of 26.6°. The roof area is 1,344 × √1.25, which the calculator shows as 1,502.64 sq ft or 139.6 m². That is 15.0264 squares, or 16.529 squares with 10% waste. At 3 bundles per square, 16.529 × 3 = 49.587, so the calculator says 50 bundles.
Frequently asked questions
What is a roofing square?
A roofing square is 100 square feet of roof surface. The calculator divides the roof area in square feet by 100. If you work in meters, it converts to square feet first, using 1 ft = 0.3048 m, so the 139.6 m² roof in the worked example is 15.0264 squares.
How many bundles of shingles are in a square?
That depends on the shingle. The packaging or the manufacturer's data sheet says how many bundles cover one square, so check your product's packaging and type that number into "Bundles per square". The 3 in the field is a starting value for the example, not a figure for your shingle.
How do I find my roof pitch?
Pitch is the rise in inches for every 12 inches of run. In the attic, hold a level horizontally with one end touching the underside of a rafter. Measure 12 inches along the level from that end, then measure straight up from that point to the rafter. That measurement is the rise. If you know the angle instead, the rise is 12 × tan(angle).
Does a hip roof need a different formula than a gable roof?
No, as long as every plane has the same pitch. Each plane's surface is its footprint times the same pitch factor, so the whole roof is the whole footprint times that factor, whatever its shape. If parts of the roof have different pitches, enter each part separately.
Should the area include the overhang?
Yes. Shingles cover the eaves and rakes as well as the part over the house. With "Length and width", type the overhang and the calculator adds it to all four sides. With "Footprint area", include the overhang in the area you type.
How much waste should I add?
The calculator leaves that to you. Waste depends on the roof's shape and the shingle, so check the shingle maker's installation instructions or ask your supplier or roofer. The 10 in the field is a starting value for the example. Enter 0 to see the bare roof area in squares and bundles.