What is a "square" in roofing?

One roofing square equals 100 square feet of roof surface — the standard unit contractors and shingle manufacturers use to price and order material.

How does roof pitch affect the area?

A sloped roof has more actual surface area than its footprint suggests. We multiply the footprint area by a pitch multiplier (e.g. 1.118 for a 6/12 pitch) to account for the slope, based on sqrt(1 + (rise/run)²).

Why is the default waste factor 12% instead of 10%?

Roofing typically wastes more material than flooring or paint — cuts around vents, valleys, and edges add up. 10-15% is the common industry range for a simple roof; 12% is the middle of that range, and you can raise it for a more complex roof shape.

Does this calculator tell me how many shingle bundles to buy?

Not yet. Bundles per square vary too much by shingle type and weight (commonly 3, but up to 6 for some heavier products), so this tool sticks to squares for now — the number contractors bid and price by.

Roofing Calculator

Calculate roofing squares from your house footprint and roof pitch, including waste factor.

How we calculate it

Roof area = Footprint length × Footprint width × Pitch multiplier, Squares = ceil(Roof area × (1 + Waste factor) / 100).

Understanding your estimate

Order shingles off the wrong area and one of two things happens. Order too little and the crew stops mid-afternoon waiting on a supply run, with a roof half torn open. Order for the house footprint alone, ignoring how much a sloped roof actually stretches that surface, and you're short before the first bundle goes up. This calculator starts from the footprint you already have, the flat rectangle a foundation survey or a plot plan shows, and does the pitch math on top of it instead of asking you to already know the roof's real area.

A 40 by 30 footprint, 6/12 pitch

Say the house footprint is 40 ft by 30 ft, the roof pitch is 6/12, and the waste factor stays at its 12% default.

Footprint area: 40 × 30 = 1,200 ft².
Pitch multiplier for 6/12, pulled from a fixed table rather than computed on the fly: 1.118.
Roof area: 1,200 × 1.118 = 1,341.6 ft². This number is never rounded internally, only formatted for display.
Add the waste factor: 1,341.6 × 1.12 = 1,502.59 ft².
Divide by 100, since one roofing square is 100 ft², and round up: 15.03 becomes 16 squares.

Why the waste factor defaults to 12%, not 10%

Concrete, mulch, gravel, tile, flooring, and drywall all default their waste factor to a flat 10% in this catalog. Roofing doesn't share that number, and that's not an oversight. Roof waste convention runs 10-15% for a simple gable roof, and climbs past 20% on a roof cut through with hips and valleys that eat more shingle in trimming and overlap. Twelve percent sits in the middle of that 10-15% range, the same way this catalog's Paint Calculator settles its coverage figure at the midpoint of a manufacturer's published range rather than picking either end. It's still a field you can raise or lower, not a number locked into the formula.

One waste factor instead of a shape selector

There's no dropdown here for roof shape, no toggle between a simple gable and a hip roof full of valleys. A single waste factor absorbs that difference instead. A plain rectangular roof can sit near the bottom of the 10-15% range; a roof with more hips, valleys, and cut shingle can push toward 15% or past it. One editable number does the work two separate inputs would otherwise do, as long as it's honest about the range it needs to cover, and the hint text next to the field says so directly.

Why pitch has its own dropdown, separate from the unit toggle

Switching this calculator to metric changes the footprint fields from feet to meters, but it leaves the pitch dropdown untouched. A roof pitch written as rise over a 12-inch run, 6/12, 9/12, is American carpentry shorthand, not a measurement of length, so it has no business sitting under an imperial/metric toggle. The same twelve fixed values, from flat to 12/12, apply whichever unit system the rest of the form is in, and each one maps to a multiplier pulled from a fixed table rather than trigonometry run live in the browser.

What this calculator stops at: squares, not bundles

The result stops at squares, roofing's own unit, 100 ft² of finished surface. It doesn't go the extra step of converting that into a shingle bundle count. Three bundles per square is the number most commonly cited, but it only holds for standard three-tab or lighter architectural shingles; heavier products can run anywhere from three to six bundles per square, and getting that right would mean adding a shingle product picker this calculator doesn't have yet. Squares are also what most suppliers quote and price by, so the number here is already the one you'd read off to a supplier over the phone.