Roofing Shingle Calculator
A roofing shingle calculator divides roof area by 33.3 sq ft per bundle and rounds up. A 600 sq ft roof needs 18 bundles, or 20 with 10% waste.
One bundle of most standard shingles covers about 33.3 sq ft, so three bundles cover one 100 sq ft roofing square. Owens Corning and IKO list this coverage on their product pages.
A roofing shingle calculator divides the roof’s surface area by what one bundle covers. Three bundles cover a 100 sq ft roofing square, so one bundle covers 33.33 sq ft. A 600 sq ft roof is 600 ÷ 33.33 = 18 bundles. With 10% waste it is 19.8, which rounds up to 20.
The formula in plain words
Find the roof’s real surface area. Divide it by 33.33. Round up to a whole bundle.
The waste box multiplies the bundle count by 1.10 first and then rounds. That extra covers the shingles you cut at valleys, hips, and edges and the odd one that is damaged.
The surface area is not the footprint of the house. A sloped roof has more area than the ground under it, so a house footprint has to be multiplied by a pitch factor first.
Worked examples
Example 1, the default: a 30 ft by 20 ft roof section, $35 per bundle.
- Area: 30 × 20 = 600 sq ft
- Bundles: 600 ÷ 33.33 = 18.0
- Cost: 18 × $35 = $630
- With 10% waste: 19.8, rounded up to 20 bundles, or $700
Example 2, a whole house roof: 45 ft by 30 ft of roof surface.
- Area: 45 × 30 = 1,350 sq ft
- Bundles: 1,350 ÷ 33.33 = 40.5, rounded up to 41, or $1,435
- With 10% waste: 44.55, rounded up to 45 bundles, or $1,575
If you start from the footprint, convert first. A 40 × 30 ft footprint at 6/12 has a surface of 40 × 30 × 1.118 = 1,341.6 sq ft. To enter it here, use a length of 40 and a width of 33.54.
Bundles by roof area
| Roof surface area | Squares | Bundles | With 10% waste |
|---|---|---|---|
| 300 sq ft | 3 | 9 | 10 |
| 600 sq ft | 6 | 18 | 20 |
| 1,000 sq ft | 10 | 30 | 33 |
| 1,200 sq ft | 12 | 36 | 40 |
| 2,000 sq ft | 20 | 60 | 66 |
How to measure
Measure each roof plane’s length along the ridge and its width up the slope, and add the areas. If you cannot climb up, measure the footprint, including overhangs, and multiply by the pitch factor for your slope. The roof area calculator does this, and the hip roof calculator handles a four-sided roof.
Subtract nothing for chimneys or skylights on a first pass. Their flashing and cuts use shingles that offset the area they remove.
Common mistakes
- Entering the house footprint as the roof area.
- Skipping waste on a roof with many valleys, dormers, or hips.
- Forgetting the extras. Ridge cap, starter strip, underlayment, nails, drip edge, and flashing are all separate. The roofing underlayment calculator and the ice and water shield calculator cover two of them.
- Assuming three bundles per square for every product. Check the label.
- Pricing a tear-off as if the old layer were already gone. Removal and disposal are a separate cost, which the roofing cost calculator can estimate.
Adding up two roof sections
Say a house roof has 45 × 30 ft of surface and an attached garage has 24 × 14 ft.
- House: 1,350 sq ft
- Garage: 24 × 14 = 336 sq ft
- Total: 1,686 sq ft
- Bundles: 1,686 ÷ 33.33 = 50.58, rounded up to 51, or $1,785 at $35
- With 10% waste: 55.64, rounded up to 56 bundles, or $1,960
Run both sections as one total instead of rounding each separately, which can overbuy by a bundle.
Checking the order against the bundles
Before you order, look at the label on the product. It lists the coverage of each bundle and the number of bundles in a square. If a bundle covers 33.3 sq ft, the calculator is right. If the label says four bundles to a square, each bundle covers 25 sq ft, and the 1,350 sq ft roof needs 54 bundles before waste instead of 41. Always use the manufacturer’s number.
Related calculators
Start with the roof pitch calculator to find your slope. The roofing cost calculator prices the full job including labor.
Frequently asked questions
How many bundles of shingles do I need?
Divide the roof surface area in square feet by 33.3 and round up. A 1,350 sq ft roof is 40.5 bundles, so you buy 41, and with the 10% waste box ticked it is 44.55, so 45. This assumes three bundles cover one 100 sq ft roofing square.
Should I enter roof footprint or actual roof surface area?
Enter the surface area. A footprint of 40 × 30 ft at a 6/12 pitch becomes 40 × 30 × 1.118 = 1,341.6 sq ft of roof. Entering the 1,200 sq ft footprint would leave you about 4 bundles short before waste. The roof area calculator finds the surface from the footprint and pitch.
Why does this calculator round up to a whole bundle?
Bundles are sold whole. A 1,350 sq ft roof comes to 40.5 bundles, and 41 is the first amount that covers it. Rounding down would leave a strip of bare roof.
Should I add extra for waste?
Yes. The 10% box adds cut waste around valleys, hips, vents, and edges, and takes 600 sq ft from 18 bundles to 20. Complex roofs with many hips and valleys waste more. Many roofers also buy ridge cap, starter strips, and underlayment as separate items.
Are all shingles three bundles to a square?
Standard architectural shingles are commonly three bundles per square, which is what this calculator uses. Some heavier or premium shingles come four or more per square. Read the bundle label for its coverage and adjust the count if it differs.
How many square feet does a bundle of shingles cover?
A standard bundle covers about 33.3 sq ft, and three bundles make one 100 sq ft roofing square. Owens Corning and IKO list this on their product pages. Heavier or laminated shingles can differ, so read the coverage on your product label.
Estimates only. Verify quantities with your supplier before purchasing.