Shingle Calculator
Estimate shingles from the ground. Enter the building footprint length and width in feet, pick the roof pitch, and set a waste factor to get roof area in square feet, roofing squares, and how many bundles to order.
Example: with Footprint length (ft, incl. eave overhangs) 40 · Footprint width (ft, incl. eave overhangs) 30 · Roof pitch 6/12 (×1.118) · Waste factor (%) — 10 gable, 15 hips/valleys 10 → Shingles to order: 14.8 squares (incl. waste).
- Roof surface area (before waste)1,342 sq ft
- Bundles (3 per square)45 bundles
Computed by the calculator below using its default values. Change any input to see your own numbers.
One roofing square = 100 sq ft = 3 bundles of standard shingles. Footprint × pitch multiplier gives true roof area without climbing up.
Squares, bundles, and the pitch multiplier
Roofers sell and quote by the square: 100 square feet of roof surface. Standard three-tab and most architectural shingles pack 3 bundles to the square, so each bundle covers about 33 square feet. The hard part of estimating is that the roof surface is bigger than the building footprint because it slopes. Multiply the footprint by the pitch factor — 1.118 for a 6/12 roof — to get true surface area. A 40 × 30 footprint at 6/12 is 1,200 × 1.118 ≈ 1,342 square feet, call it 13.5 squares before waste.
Measure the footprint to the roof edges, not the walls: eave and rake overhangs are shingled too, and skipping them shorts a typical house by a square or more.
How much waste to add
On a simple gable roof, 10% covers cut loss at rakes, starter courses, and a few broken shingles. Hip roofs, valleys, dormers, and anything cut up deserve 15%, because every hip and valley generates angled offcuts. Ridge caps and starter strips are technically separate products; many crews cut them from field shingles, which the waste factor absorbs on small roofs. Bundles round up to whole bundles because that is how they are sold.
How it’s calculated
Roof area = footprint length × width × pitch multiplier, where the multiplier = √(12² + pitch²) ÷ 12 (1.118034 for 6/12). Squares = area × (1 + waste%) ÷ 100. Bundles = squares × 3, rounded up. Coverage convention: 1 square = 100 sq ft, 3 bundles per square (standard strip shingles).
Assumes the whole footprint is under one pitch and that your shingle packs 3 bundles per square — some heavyweight architectural lines run 4 or 5 bundles per square, so check the wrapper.
Roof area of a 1,200 sq ft footprint by pitch
| Pitch | Multiplier | Roof surface |
|---|---|---|
| 3/12 | 1.031 | 1,237 sq ft |
| 4/12 | 1.054 | 1,265 sq ft |
| 6/12 | 1.118 | 1,342 sq ft |
| 8/12 | 1.202 | 1,442 sq ft |
| 12/12 | 1.414 | 1,697 sq ft |
Computed with multiplier = √(144 + pitch²) ÷ 12 applied to a 1,200 sq ft footprint; rounded.
Common mistakes
- Using footprint area without the pitch multiplier — an 8/12 roof is 20% bigger than its footprint.
- Measuring to the walls instead of the roof edges, which leaves out the overhangs you also have to shingle.
- Running 10% waste on a hip roof with valleys — cut-up roofs eat 15% or more.
- Assuming every product is 3 bundles per square; some architectural and designer shingles take 4+.
Frequently asked questions
What is the formula for shingles needed?
Squares = length × width × pitch multiplier × (1 + waste) ÷ 100. The multiplier is √(144 + pitch²) ÷ 12 — for a 6/12 roof, 1.118. Multiply squares by 3 for bundles.
How many bundles of shingles are in a square?
Three bundles per square for standard shingles, so each bundle covers about 33 sq ft. Some thick architectural products pack 4 or more bundles per square — the coverage printed on the wrapper wins.
How much waste should I add for a hip roof?
Use 15% for hips, valleys, and dormers, versus 10% for a plain gable. Every hip and valley line produces angled offcuts that cannot be reused, and complex roofs also burn more ridge cap.
Do I include overhangs in the footprint?
Yes — measure to the drip edge, not the exterior walls. A house with 12-inch overhangs on a 40 × 30 wall plan actually presents a 42 × 32 footprint to the sky, about 144 extra square feet of shingles.