Roofing Calculator — squares and shingle bundles

How it works

Roofers measure area in squares, where one square is 100 square feet of roof surface. To find how much material you need, convert the roof area to squares, adding a waste allowance:

squares = roof area × (1 + waste) ÷ 100

Then convert squares to bundles of shingles. Most asphalt shingles come 3 bundles to the square, so:

bundles = ⌈squares × bundles-per-square⌉

The bundles-per-square is an input (usually 3, but heavier architectural shingles can be 4 or 5). A 10% waste allowance covers cuts, ridges, hips and starter courses — use 15% for a complex roof with many valleys and dormers. Bundles round up.

Measure the actual roof surface, not the building footprint — a pitched roof has more area than the floor below it, so multiply the footprint by a pitch factor first if that is all you have.

Worked example

A 2000 sq ft roof with 10% waste is 2000 × 1.1 ÷ 100 = 22 squares. At 3 bundles per square that is ⌈22 × 3⌉ = 66 bundles. A small 200 sq ft shed roof is 2.2 squares, or 7 bundles. A 3000 sq ft cut-up roof with 15% waste comes to 34.5 squares and about 104 bundles.

Frequently asked questions

What is a roofing square?

A roofing square is 100 square feet of roof area — the standard unit roofers and suppliers use. A 2000 sq ft roof is 20 squares before waste. Shingles and underlayment are sold and priced by the square.

How many bundles of shingles are in a square?

Usually 3 bundles per square for standard three-tab asphalt shingles. Heavier architectural or designer shingles run 4 or even 5 bundles per square because each bundle covers less. Check the product; it is an input here.

How do I measure my roof area?

Measure the actual sloped surface, not the footprint of the house. If you only have the footprint, multiply by a pitch factor (about 1.12 for a 6/12 pitch, 1.25 for 9/12) to get the true roof area, then enter that.

How much waste should I allow for roofing?

About 10% for a simple gable roof, covering cuts, the starter course, and ridge and hip caps. Complex roofs with many valleys, hips and dormers waste more — allow 15%. Very cut-up or steep roofs can go higher.

Does this include underlayment, ridge caps or nails?

No — it sizes the field shingles by the square and bundle. Underlayment is bought by the square (same area), ridge and hip caps by the linear foot, and nails and accessories separately. Estimate those on their own.

Why measure in squares instead of square feet?

Tradition and convenience — 100 sq ft is a handy unit for a large roof, and all roofing materials (shingles, underlayment, labor) are quoted per square. Working in squares keeps the math simple: divide the area by 100.