Roofing Calculator
Convert a roof footprint and its pitch into roofing squares, shingle bundles, and underlayment rolls — with a waste allowance for cuts and ridges — so you order the right materials for a re-roof or new build.
How to Use
- Enter the roof footprint length and width in feet (the building dimensions, not the sloped surface).
- Select the pitch (rise per 12 inches of run) so the tool can convert the flat footprint into actual sloped roof area.
- Set a waste percentage — about 10–12% for a simple roof, 15% or more for steep, cut-up, or hip roofs.
- Read the roofing squares, shingle bundles, and underlayment rolls in the results panel.
- Check the step-by-step Show Work below to see how pitch and waste are applied.
Show Work
Notes
About the Roofing Calculator
The Roofing Calculator gives you a fast, free answer for building, materials estimation and site work without sending anything off your device. Convert a roof footprint and its pitch into roofing squares, shingle bundles, and underlayment rolls — with a waste allowance for cuts and ridges — so you order the right materials for a re-roof or new build.
How it works
Enter your figures and the result appears instantly, updating the moment you change anything. There is no submit button and nothing to wait for, so it is easy to try a few what-if numbers and compare the results. Just check each box holds the kind of value it expects.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
What is a roofing square?
A square is 100 square feet of roof coverage — the standard unit roofers and suppliers use to quote materials and labor. Asphalt shingles come about three bundles to the square, so the tool reports both squares and bundles to make ordering straightforward.
Why does pitch change how much I need?
A steeper roof has more surface area than its flat footprint suggests. The calculator multiplies the footprint by a pitch factor — for example a 6/12 roof is about 1.12 times its footprint and a 12/12 roof about 1.41 times. Skipping this step would badly under-order your shingles.
How many bundles of shingles per square?
Standard three-tab and most architectural shingles run three bundles per square, so a 20-square roof needs about 60 bundles plus waste. Heavier designer shingles can take four or five bundles per square — check the wrapper. This tool uses the common three-bundle rate.
How much waste should I add?
Plan on roughly 10% for a simple gable roof and 15% or more for hip roofs, lots of valleys, dormers, or steep pitches that need extra cuts and ridge caps. Buying a little extra also keeps matching shingles from the same lot on hand for future repairs.
What about underlayment, drip edge, and starter strip?
The calculator estimates underlayment rolls (commonly four squares per roll) along with the shingles. Don't forget the accessories a full job needs — drip edge along the eaves and rakes, ice-and-water shield in valleys and at the eaves in cold climates, starter strip, and ridge cap. Measure those linear runs separately.
How do I use the Roofing Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
Re-roofing a house
Turn building dimensions and pitch into squares and bundles so you order the right shingle count for a tear-off.
Pricing a roofing job
Get squares up front, the unit roofers quote in, to compare bids and budget materials.
Estimating a steep roof
Apply the pitch factor so a steep roof is not under-ordered based on its smaller footprint.
Ordering underlayment
See how many underlayment rolls the roof area needs alongside the shingles.
Planning a garage or outbuilding roof
Size a small low-slope roof and order just enough shingles and underlayment.
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