🏠 Roofing Shingle Calculator

Enter your roof footprint dimensions and pitch to estimate roof surface area, roofing squares, and bundles of shingles needed.

Roof Footprint Length (ft)

Roof Footprint Width (ft)

Pitch (rise per 12" run)

Waste Allowance (%)

Footprint, pitch, squares, bundles

A sloped roof covers more surface than the ground it sits over, and the pitch multiplier is what converts between them. It comes straight out of Pythagoras on a triangle 12 in along the run and the rise you enter. The padded area is then divided by 100, because a roofing square is 100 sq ft, and multiplied by three bundles per square.

multiplier = sqrt(1 + (rise / 12)^2)
roof area  = footprint x multiplier
squares    = roof area x (1 + waste% / 100) / 100
bundles    = ceiling(squares x 3)

A 40 x 30 ft footprint at 6/12 has a multiplier of 1.118, so 1,200 sq ft on the ground is 1,342 sq ft of roof. With 10% waste that is 14.8 squares and 45 bundles.

Pitch	Multiplier	1,200 sq ft footprint becomes
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

What the bundle count leaves out

Starter strip and ridge caps are extra. Neither comes out of the field shingles in this count, and hip and ridge caps add up quickly on a complex roof.
Not every shingle is three bundles to the square. Heavy architectural and designer shingles run four or five, so check the wrapper before you convert squares into bundles.
Valleys and hips cut every course at an angle, and the offcuts are triangles. 10% suits a plain gable roof; 15% is closer for a hipped or cut-up roof, and complex rooflines go higher still.

Measure the footprint including the overhangs, not the walls, and split an L-shaped or multi-pitch roof into rectangles and run each one separately - a single average pitch across two different slopes gets both wrong. Order the whole job in one delivery so the shingles come from the same production run; colour blends drift between batches, and a patch of slightly different shingles shows badly on a large slope.

Underlayment, drip edge, flashing and any ice barrier at the eaves are all separate materials, and several of them are not optional. How many layers of shingles may stay on the deck, where an ice-and-water membrane is required and whether the job needs a permit and inspection are all set by your local building rules, and those override the material list here.

Frequently asked questions

How many bundles of shingles for a 30x40 roof?

At 6/12 pitch, 1,342 sq ft of roof surface, which is 14.8 squares and 45 bundles with a 10% allowance. A steeper 10/12 roof over the same footprint needs about 52 bundles.

What is a roofing square?

100 sq ft of finished roof surface. Shingles are sold and quoted in squares because it makes labour and material comparable, and standard three-tab and most architectural shingles come three bundles to the square.

How do I find my roof pitch without going up there?

Hold a level out from the roof edge, mark 12 in along it, and measure down to the roof surface - that drop is the rise. From inside an attic, do the same against a rafter. 4/12 to 6/12 covers most modern houses.