Roof Shingle Calculator
House footprint and pitch in — true sloped roof area, squares and bundles out, waste included.
The short answer
Formula. Squares = footprint area × pitch multiplier × (1 + waste) ÷ 100; bundles = squares × 3 for standard three-tab shingles.
Example. A 30 ft × 40 ft house at 6/12 pitch (multiplier 1.118) with 10% waste is 14.76 squares — 45 bundles.
How this calculator works
Roofers sell by the square — 100 sq ft of roof — so the whole calculation is turning your house into honest squares. Start with the footprint: length × width. That is not the roof area, because the roof is sloped. Each face's true surface is its flat projection stretched by the pitch multiplier, which is just the Pythagorean theorem: a 6/12 pitch face rises 6 in per 12 in of run, so its sloped length is √(12² + 6²) ÷ 12 = 1.118 times the flat width. Two faces cancel out, leaving footprint × multiplier: a 30 × 40 footprint (1,200 sq ft) at 6/12 is about 1,342 sq ft of shingled surface.
From there, add waste and divide. Waste is not padding, it is the diagonal cuts at valleys and hips, the starter course along eaves, and the imperfect reality of a hip roof's corners — 10% for a simple gable, 15% for hip roofs or roofs with dormers and valleys. Then squares (area ÷ 100) times bundles-per-square (3 for standard architectural shingles; some heavyweight designer lines take 4 or more — the calculator takes that as an input). The 30 × 40 example: 1,342 × 1.10 ≈ 1,476 sq ft ≈ 15 squares = 45 bundles, plus ridge caps and underlayment below.
What the simple footprint model leaves out, and why pros still measure the roof itself: overhangs (include them by measuring eave-to-eave, or add 1–2 ft per side to the footprint), dormers and additions (measure each as its own little roof and add), and the garage wing. Underlayment, ice-and-water shield at eaves and valleys, drip edge, and ridge vents are sold by roll and linear foot — one synthetic underlayment roll covers roughly 10 squares, and a bundle of field shingles cut into caps caps about 35 linear ft of ridge and hip. Steep-pitch roofs above 8/12 and second stories cost more to install per square, not to buy — the bundle count is identical.
Sources & review date
- Three bundles per square applies to standard three-tab shingles; architectural lines vary — bundles-per-square is an editable input.
- The pitch multiplier is Pythagoras: for 6/12 it is √(6²+12²) ÷ 12 = 1.118.
Last reviewed: October 2026. Numbers that drift (fees, prices, densities) are editable inputs on this page.
Roof shingle FAQs
How do I measure my roof without climbing it?
The footprint method: measure the building's length and width at ground level (or from an aerial photo), add the overhang (about 1–2 ft total per side), pick your pitch from the attic or a gable end, and multiply by the pitch multiplier here. It lands within a bundle or two on simple roofs.
How many shingles for a 1,000 sq ft roof?
If 1,000 sq ft is the footprint at 6/12, the roof is 1,118 sq ft of surface; with 10% waste that is 12.3 squares — 37 bundles at 3 per square, plus cap shingles and starter.
Do I need more shingles for a hip roof?
Yes — hips generate diagonal scrap at every corner junction, so use 15% waste instead of 10%. Hips also add cap linear feet: measure hip and ridge lengths together for your cap bundles.
Can I use 3 bundles per square for any shingle?
No. Standard 3-tab and most architectural shingles are 3 per square, but premium designer shingles can be 4–6 per square because each bundle covers less. The bundle label states coverage — enter that number of bundles per square in the calculator.