Roof Shingle Calculator
Enter your measurements
Extra to cover cuts, breakage, and mistakes.
Results
- Shingle bundles45 bundles
- Roofing squares14.76 squares
- Underlayment rolls210 sq ft synthetic rolls
- Starter bundles5
- Roofing nails37 lb
Estimated cost
per roofing square of asphalt shingles (material only)
Material cost is per roofing square (100 sq ft) of asphalt shingles only; the low end reflects entry-level three-tab, the high end mainstream 30-year architectural shingles. Installed cost per square includes tear-off of one existing layer, synthetic underlayment, starter strip, and labor; figures near the high end reflect steep-pitch surcharges, coastal markets, and multi-story homes.
Estimate only — prices vary by region, supplier, and season. Get a local quote before buying.
This shingle roofing calculator converts your building footprint and roof pitch into the exact materials you need to order: shingle bundles, roofing squares, underlayment rolls, starter bundles, and nails, with a configurable waste allowance built in. It matters because shingles are sold by the bundle (three bundles cover one square, which equals 100 square feet of roof surface), and pitch dramatically changes how much actual roof surface you have versus your floor footprint. A 6/12 pitch adds about 12 percent more area than the flat footprint; a steep 12/12 adds roughly 41 percent. Beyond bundles, the calculator catches the secondary materials that are easy to forget: starter strip bundles for the eave and rake edges, underlayment rolls (synthetic rolls cover about 10 squares each, while 15 lb felt covers roughly 4 squares), and nails priced by the pound. Standard waste for a simple gable is 10 percent; roofs with dormers, valleys, or multiple hips typically need 15 to 20 percent. Pinning down these numbers before you reach the supply yard prevents both short orders that stall the job and excess returns that trigger restocking fees.
How it’s calculated
Roof area = Footprint × slope multiplier. Squares = area ÷ 100. Bundles = squares × 3 (industry standard), plus waste.
Worked example
For a 40 ft by 30 ft building with a 6/12 pitch, the footprint is 1,200 sq ft, which the 6/12 slope multiplier (1.118) stretches to about 13.42 squares of actual sloped roof. Adding the 10 percent waste allowance brings the order to 14.76 roofing squares, which rounds up to 45 shingle bundles. The same job needs 2 synthetic underlayment rolls, 5 starter bundles for the eave and rake edges, and roughly 37 lb of roofing nails, all produced together so you can build a single purchase list.
Inputs
- Building length
- 40 ft
- Building width
- 30 ft
- Roof pitch (rise per 12)
- 6 /12
- Waste / overage
- 10 %
Result
- Shingle bundles
- 45 bundles
- Roofing squares
- 14.76 squares
- Underlayment rolls
- 2
- Starter bundles
- 5
- Roofing nails
- 37 lb
- Estimated material cost
- $1,550 – $2,509
Materials & pricing near you
Asphalt shingles are sold by the bundle at every home center and roofing supply house in the US, and both three-tab and architectural (dimensional) shingles follow the three-bundles-per-square standard, though some premium designer lines run four bundles per square, so confirm the coverage on the product label before ordering. Pricing swings with region: supply houses in the South and Midwest generally run lower per square on architectural shingles than coastal metros, where freight and local markup push materials higher. Demand spikes after major hailstorms can temporarily inflate both prices and lead times at regional distributors. Most supply houses set a delivery minimum, and big-box stores often charge a flat rooftop-delivery fee that makes a contractor account worthwhile on larger jobs. A building permit is required in most jurisdictions for a full tear-off, and rules on re-roofing over an existing layer vary by county.
Frequently asked questions
How many shingle bundles do I need per square?
Three bundles cover one roofing square (100 sq ft of sloped roof) for standard three-tab and most architectural shingles. Some heavier designer or laminated shingles need four bundles per square, so always check the coverage line on the bundle label or product data sheet before ordering. Buying on the three-bundle assumption for a four-bundle product leaves you 25 percent short and forces a second trip mid-job.
How do I find my roof pitch from the ground?
Measure the building footprint (the outside length and width of the exterior walls) for the calculator, then estimate pitch with a phone pitch-finder app held against a rake board, or read it directly with a level: set a 2-foot level against the roof deck, hold it dead level, and measure the vertical drop from the 12-inch mark down to the deck. That rise is the first number in your X/12 pitch. This calculator takes pitch as rise per 12 of run, so a 6-inch rise over 12 inches is 6/12.
What waste percentage should I use?
Use 10 percent for a simple two-slope gable with no penetrations. Bump it to 15 percent for a hip roof or a gable with one or two skylights, and 20 percent or more for complex roofs with multiple valleys, dormers, or steep pitches above 10/12, where cuts around features generate real scrap. Erring low is the costlier mistake: shingles from a different production run can show slight color variation, so under-ordering and rebuying later risks a visible mismatch on the roof.
Do I need a permit to replace my roof?
In most US jurisdictions a full tear-off and re-roof requires a building permit, and an inspector typically checks decking and flashing at rough and final stages. Some localities still allow one new layer over existing shingles without a permit, but many now prohibit layering because of added dead load and updated codes, so check with your local building department first. Skipping a required permit can also complicate a homeowner's insurance claim if storm damage occurs later.