Roofing Calculator
Calculate shingles, bundles, and materials needed for your roof.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Roofing Calculator
This calculator converts your roof dimensions into the exact materials you need to order, accounting for pitch, waste, ridge caps, and starter strip. Here is how to use it:
- Enter your roof length and width. These are the footprint dimensions of the roof section, measured at the base. For a simple gable roof, measure the length and width of the building at the eaves. If you have multiple roof sections, calculate each section separately and add the results.
- Select the roof pitch. Pitch is expressed as rise over run, such as 6/12 (rises 6 inches for every 12 inches of horizontal run). A steeper pitch means more actual surface area than the footprint. The calculator applies the correct pitch factor automatically. If you are unsure of your pitch, measure the rise over an 18-inch horizontal run with a level.
- Set a waste factor. The standard waste factor is 10% for a simple gable roof. For complex roofs with hips, valleys, dormers, or many cuts, use 15-20%. Never order without a waste allowance.
- Enter the ridge length. This is the total length of the peak (ridge) of the roof. The calculator determines how many bundles of ridge cap shingles you need, based on the standard coverage of 35 linear feet per bundle.
Results update live as you type. Use Share to send a pre-filled link to a contractor or supplier, or Copy to grab the summary for a materials list.
About Roofing Squares and Shingle Calculations
Roofing materials are ordered in squares. One square covers 100 square feet of roof surface. Standard three-tab and architectural (dimensional) shingles come in bundles that weigh around 65-80 pounds each, with three bundles covering one square. That is why this calculator multiplies squares by three to get bundle count.
Pitch matters because the actual surface area of a sloped roof is always larger than the footprint area. A flat roof has a pitch factor of 1.0. A 6/12 pitch has a factor of 1.118, meaning a roof that covers 1,200 square feet of floor area actually has 1,342 square feet of shingles to cover. Skipping this step leads to being short on materials.
Starter strip is the first course of shingles laid along the eaves before the first full course. One roll typically covers about 100 linear feet of eave. This calculator estimates starter strip from the eave perimeter (two sides of a gable roof). Adjust for your specific roof shape.
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Frequently Asked Questions
How many bundles of shingles do I need per square?
Standard asphalt shingles, both three-tab and architectural (dimensional), require three bundles to cover one square (100 square feet). Some heavier or specialty shingles may require four bundles per square. Always check the bundle coverage listed on the shingle package. This calculator uses the standard three-bundles-per-square formula.
What waste factor should I use for roofing?
For a simple gable roof with no dormers or complex cuts, 10% is the standard waste allowance. For a hip roof, add 15%. For a complex roof with multiple valleys, dormers, or skylights, use 15-20%. It is almost always cheaper to have a few extra bundles than to pay for a second delivery. Leftover shingles also serve as future repair material.
How do I measure roof pitch?
The easiest method is from inside the attic. Hold a level horizontally against a rafter and measure 12 inches along the level from the rafter. Then measure straight up from the end of that 12-inch mark to the rafter. That vertical measurement is the rise. A 6-inch rise over 12 inches of run is a 6/12 pitch. From the outside, you can also place a level on the roof surface and measure the rise over 12 inches of run along the level.
What is the difference between squares and bundles?
A square is a unit of roofing coverage equal to 100 square feet. A bundle is a physical package of shingles. For standard shingles, three bundles equal one square. Roofing contractors and suppliers quote prices per square. Lumber yards and home improvement stores sell by the bundle. When ordering, convert your squares to bundles and always round up to a whole number.