Calculator + chartEnter your measurements below and it works the answer out.
A roofing square is 100 sq ft. How many bundles make one is not fixed — three is common, but heavier shingles run four or five, so it is a setting here rather than a built-in constant.
| Roof pitch | Multiplier | Bundles per square | Coverage per bundle |
|---|---|---|---|
| 3/12 | 1.031 | 3 | 33.3 sq ft |
| 4/12 | 1.054 | 3 | 33.3 sq ft |
| 5/12 | 1.083 | 4 | 25.0 sq ft |
| 6/12 | 1.118 | 4 | 25.0 sq ft |
| 7/12 | 1.158 | 5 | 20.0 sq ft |
| 8/12 | 1.202 | 5 | 20.0 sq ft |
| 10/12 | 1.302 | — | — |
| 12/12 | 1.414 | — | — |
The multiplier column is geometry — the square root of 1 plus (rise ÷ 12) squared — and applies to every product. The bundle columns are NOT paired with the pitch beside them: they simply show what 3, 4 and 5 bundles per square work out to. Your product's figure is on the wrapper.
A square is 100 square feet. That is the unit the whole exterior trade quotes in and it does not vary. Everything else on this page does.
Footprint or roof surface — the calculator asks, and you should know which you have. If you measured the building from the ground, that is the footprint, and the roof above it is longer up the slope. If you measured on the roof itself, or off a drawing of the roof planes, that is already the surface and applying a pitch multiplier to it would over-order. Silently assuming one or the other is how a roof order goes wrong by twelve per cent.
The pitch multiplier is geometry. A roof rising R inches over 12 inches of run has a slope length of √(12² + R²) for every 12 inches of run, so the factor is √(1 + (R ÷ 12)²). A 6/12 roof is 1.118 times its footprint and a 12/12 roof is 1.414. You can check any of these on a calculator.
Bundles per square is a product figure, not a constant. Three bundles to a square is common for three-tab and many architectural shingles, which works out at 33.3 sq ft a bundle. Heavier architectural products run four (25 sq ft) and designer products five (20 sq ft). The wrapper and the manufacturer's specification are the authority — this page asks you rather than assuming.
Ten per cent waste, and more on a complicated roof. The allowance covers cuts at hips, valleys and rakes. A simple gable roof uses less; a roof with dormers, hips and multiple valleys can want fifteen. Starter course, ridge caps and underlayment are separate purchases and are not included here.
Divide the roof surface area by 100. If you measured the building footprint from the ground rather than the roof itself, multiply by the pitch factor first — a 40 by 30 ft footprint is 1,200 sq ft, and on a 6/12 pitch the roof surface is 1,342 sq ft, or 13.4 squares before waste.
Usually three, at 33.3 sq ft each, but not always. Heavier architectural shingles run four bundles to a square and designer products five, which is 25 and 20 sq ft a bundle. Check the wrapper — assuming three on a five-bundle product leaves you 40% short.
Only if you measured the building footprint from the ground. If you measured the roof planes themselves, the pitch is already in your number and multiplying again over-orders. This calculator asks which you have rather than guessing.
Pythagoras. A roof rising R inches per 12 inches of run has a slope length of the square root of (12² + R²) for each 12 inches, so the factor is √(1 + (R÷12)²). A 6/12 roof gives 1.118.
Ten per cent on a straightforward gable roof. Fifteen on a roof with hips, valleys and dormers, where every cut leaves an offcut too small to use. Starter strip, ridge cap and underlayment are ordered separately.
Free to use on any site, including commercial ones. Paste this where you want it to appear — it keeps working when we update the figures.