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Roofing calculator

Your roof area, squares, shingle bundles and the main accessories to order, from the ground.

Example sizes, change them. The answer updates as you type.

Along the ridge. Measure the outside walls from the ground.

Inches of rise per 12 inches of run. Not sure? Use the roof pitch calculator.

How far the roof sticks out past the wall. 12 inches is only an example: measure yours.

Roof shape
= 16.6 squares Full breakdown below
You need
16.6 squares
includes 10% waste6/12 gable roof
50 shingle bundles
1,503 ft² of roof
1.118 pitch factor

Add it to build one shopping list for your whole job.

Checked by JunaydMethod and sources

Your roof Drawing of your gable roof on a house 40 feet long and 30 feet wide, at a 6/12 pitch. The walls are drawn at a fixed height, not to scale. 30 ft 40 ft 6/12 pitch
Redraws as you typewalls not to scale

Order 16.6 squares (50 bundles) plus the accessories below.

How many bundles of shingles do I need?

To work out roofing materials, multiply the house footprint plus overhang by the pitch factor for the roof area, then divide by 100 for squares. Add 10% for waste and buy 3 bundles per square. A 40 by 30 foot house with a 6/12 roof needs 16.6 squares: 50 bundles.

How we worked it out

  1. (40 ft + 2 × 12 in) × (30 ft + 2 × 12 in) = 42 ft × 32 ft = 1,344 ft²
  2. 1,344 ft² × 1.118 (6/12 pitch factor) = 1,503 ft² of roof
  3. 1,503 ft² ÷ 100 ft² per square = 15.03 squares
  4. 15.03 squares + 10% waste = 16.53, so 16.6 squares (rounded up)
  5. 16.6 squares × 3 bundles = 49.8, so 50 bundles (rounded up)
  6. Edges: eaves 84 ft, rakes 71.6 ft, ridge 42 ft

Everything else this roof needs

  • Starter stripeaves and rakes, 105 feet per bundleoften forgotten 2 bundles
  • Ridge and hip cap25 feet per bundleoften forgotten 2 bundles
  • Underlayment929 square feet per roll 2 rolls
  • Drip edgeeaves and rakes, 10 foot piecesoften forgotten 16 pieces
  • Ice barrierturn it on in More options if ice dams happen where you liveoften forgotten
  • Roofing nailsfield shingles only, 4 per shingle 3,984-5,312
  • Pipe boots, vents and flashingcount your own: we can't see them

What is a pitch factor?

A pitch factor turns the flat footprint of a roof into its true sloped area. It is the square root of 1 plus the rise over 12, squared. A 6/12 roof has a factor of 1.118, so every 100 square feet of footprint is about 112 square feet of roof.

The roof pitch calculator has the factor for every pitch from 1/12 to 12/12.

Why do gable and hip roofs need the same shingles?

A gable roof and a hip roof over the same house at the same pitch have the same area. Every slope is the footprint times the same pitch factor. What changes is the edges: a hip roof has hips instead of gable ends, so it needs more ridge cap and no rake edge.

What does the building code require?

The International Residential Code allows asphalt shingles only on roofs of 2/12 or steeper (R905.2.2). Below 4/12 it calls for two layers of underlayment. Where the local code marks a risk of ice dams, it requires an ice barrier at the eaves (R905.1.2).

Worked examples

40 x 30 feet house, gable, 6/12, 12 inch overhang, 10% waste

House length 40 ftHouse width 30 ftRoof pitch 6 /12Roof shape GableOverhang 12 inExtra for waste and cuts 10%Ice dams happen where I live no

Order 16.6 squares (50 bundles) plus the accessories below.

Squares of shingles to order
16.6
Shingle bundles
50
Roof area
1,503 ft²
Pitch factor
1.118

Same house with a hip roof: same area, more ridge cap

House length 40 ftHouse width 30 ftRoof pitch 6 /12Roof shape HipOverhang 12 inExtra for waste and cuts 10%Ice dams happen where I live no

Order 16.6 squares (50 bundles) plus the accessories below.

Squares of shingles to order
16.6
Shingle bundles
50
Roof area
1,503 ft²
Pitch factor
1.118

Low 3/12 roof: double underlayment

House length 40 ftHouse width 30 ftRoof pitch 3 /12Roof shape GableOverhang 12 inExtra for waste and cuts 10%Ice dams happen where I live no

Order 15.3 squares (46 bundles) plus the accessories below.

Squares of shingles to order
15.3
Shingle bundles
46
Roof area
1,385 ft²
Pitch factor
1.031

Common questions

How many bundles of shingles are in a square?

Most architectural and 3-tab shingles come 3 bundles to a square, and a square covers 100 square feet of roof (GAF, Owens Corning, Malarkey). Some designer shingles use 5 or 6 bundles a square, so check the wrapper.

How big is a roofing square?

A roofing square is 100 square feet of roof surface, the area of a 10 by 10 foot patch. Shingles are packed by the square, usually 3 bundles to each.

How many bundles of shingles do I need for 10 squares?

Ten squares of roof take 30 bundles of shingles at 3 bundles a square. With 10% extra for waste and cuts, order 11 squares: 33 bundles.

How much does a bundle of shingles weigh?

A square of CertainTeed Landmark architectural shingles weighs about 217 to 229 pounds, according to its data sheet. Where a square comes in 3 bundles, each bundle weighs about 72 to 76 pounds; check the wrapper for your brand.

What will the new roof cost?

See the installed price for your house and material, with tear-off and decking shown separately. Your sizes go with you.

House length 40 ftHouse width 30 ftRoof pitch 6/12Overhang 12 in

Price this roof

More roofing calculators

Method and sources

Each calculator uses the standard formula and the manufacturer's own figures, such as bag yields, and rounds up where running short would cost you a trip. Every step is shown. Cost ranges come from named surveys with the date we checked them. Spot something wrong? Tell us and we will fix it and note the change.

  • One roof plane pitch; gable and hip roofs of the same footprint and pitch have the same area.
  • 3 bundles per square (most architectural and 3-tab lines); some designer shingles use more.
  • Accessories sized with the brand that covers least, so you are less likely to run short.
  • No valleys, dormers, skylights, chimneys, vents or pipe boots; count and add those yourself.
  • Below 4/12, two layers of underlayment are included (IRC R905.2.2).