Guide · 8 min read · free tool
Roofing: How to Order Shingles Without Ordering Twice
Sep 26, 2026 · Zelpura Editorial · All guides
Roofers and DIY owners make the same two mistakes in opposite directions. They measure the footprint instead of the slope, and they forget waste. The result is either a second trip to the supplier mid-job or a pallet of shingles left in the driveway that nobody can return. Both are avoidable with one multiplication and one addition.
This calculator takes the roof length and width, the coverage per bundle, and a waste factor, and returns the area, the number of bundles, and the squares. It handles the slope conversion that most people skip, and it runs locally — no upload, no account, no waiting.
Worked example. A roof 40 feet by 30 feet. Footprint: 1,200 square feet. On a moderate slope the actual surface area is larger — apply a pitch factor, and 1,200 becomes roughly 1,400. Add 10% for waste, cuts and starter courses: 1,540 square feet. At 33 square feet per bundle that is 47 bundles, or about 15 squares. Order 48 bundles.
Measure the slope, not the floor plan. A roof is not flat, and its surface area grows with pitch. A 4/12 pitch adds about 5%, a 6/12 about 12%, a 9/12 about 25%, and a 12/12 about 41%. If you are unsure of your pitch, measure the rise and run over a 12-inch span, or use a pitch app on your phone at the eave. Getting this wrong is the single largest source of under-ordering.
Waste is not optional. Ten percent covers ordinary cuts, hips, valleys and starter courses. Complex roofs with dormers, multiple valleys and skylights need 15%. Ordering exactly the calculated amount guarantees a shortfall, because the first bundle you open will be cut into pieces that do not tile neatly.
Understand what a square is. One square is 100 square feet of roof area, and it is the unit suppliers quote. Most architectural shingles cover roughly 33 square feet per bundle, so three bundles make a square — but not always. Check the coverage printed on the bundle, because it varies by product, and enter it in the calculator.
Do not forget the accessories. Starter shingles along the eaves and rakes, ridge cap shingles along every hip and ridge, roofing nails by the pound, underlayment or felt, ice-and-water shield in cold climates, drip edge, and flashing for valleys and penetrations. These are separate line items and they are the second most common cause of a mid-job trip.
Hips and valleys consume extra. Every hip and every valley needs cut shingles, and the cuts are waste. A roof with four hips and two valleys can easily need 20% over the flat calculation. Count them before you set your waste factor, and add a bundle for each valley as a rule of thumb.
Order from one production lot. Shingle colour varies slightly between manufacturing batches, and a roof patched with shingles from a different lot shows the seam in daylight. If you must order in two stages, ask the supplier to reserve the remaining bundles from the same lot, and store them flat in a dry place.
Re-run the calculator after you have measured the actual slopes rather than estimating them, and again if you add a dormer or change the layout. Ten minutes with a tape measure and this tool is cheaper than a pallet of unwanted shingles, and considerably cheaper than a roof that leaks because the valley was short.
Frequently asked questions
How many shingle bundles do I need for my roof?
Divide your sloped roof area (footprint times pitch factor) plus waste by the coverage per bundle. Most architectural shingles cover about 33 square feet per bundle, so three bundles equal one square of 100 square feet.
What waste factor should I use for shingles?
10% for a simple gable roof, 15% for a roof with dormers or several valleys, and up to 20% for complex hip roofs. Under-ordering always costs more than a few spare bundles.
How do I calculate roof area from the footprint?
Multiply length by width, then apply a pitch factor: about 1.05 for 4/12, 1.12 for 6/12, 1.25 for 9/12 and 1.41 for 12/12. Then add your waste percentage.
What is a square of shingles?
One square is 100 square feet of roof area. Suppliers quote in squares. With typical architectural shingles at 33 square feet per bundle, three bundles make one square.
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