Asphalt shingle calculator
Asphalt is the most common residential roofing material in the US, and it is estimated in bundles per square — the figure every other number on your order hangs off.
How asphalt is measured
Asphalt shingles are counted in bundles per square (100 sq ft). Standard 3-tab shingles take 3 bundles per square; heavier architectural shingles take 4. Find your roof in squares — true area divided by 100, with waste added — then multiply by the bundles-per-square figure for your type.
Bundle and coverage math
A standard bundle covers about 33.3 sq ft, which is why three of them make a 100 sq ft square, with roughly 29 shingles in a 12-by-36-inch bundle. A 20-square roof is 60 bundles of 3-tab or 80 of architectural before waste — add 10–25% depending on roof complexity.
3-tab vs architectural
3-tab shingles are flat, uniform, and cheaper but shorter-lived; architectural shingles are layered, dimensional, longer-warrantied, and now the more common choice. The only estimating difference is the bundles-per-square figure, 3 versus 4. Pick the type that matches your roof so the count is right.
Suitable pitches
Asphalt shingles need a minimum 2:12 pitch under the IRC, and between 2:12 and 4:12 they require a doubled underlayment or a full ice-and-water shield because the shallow slope drains slowly. At 4:12 and above, a single layer of underlayment is standard. Below 2:12, shingles are not permitted — use metal or a membrane.
The rest of the order
Field shingles are only part of it. Asphalt roofs also need starter strip at the eaves and rakes, hip and ridge cap, underlayment across the deck, drip edge, and nails — four per shingle, six in high-wind zones. The full calculator lists every one of these from your measurements.
Lifespan and cost
Asphalt shingle roofs commonly last 20–30 years, with architectural at the upper end; ventilation and install quality matter as much as the shingle grade. Asphalt is the lowest up-front cost of the common materials. We publish no pricing — enter your supplier's per-square rate in the cost estimator.
Trade-offs
Lowest cost, widest availability, easy installation and repair, and the broadest contractor familiarity — against a shorter lifespan than metal, tile, or slate, and a 2:12 slope floor that rules out low-slope roofs.