Roofing Calculator

US & Canada

Enter the footprint and pitch to get the real roof area, the bundles of shingles to buy, and the underlayment and drip edge to go with them.

Your roof

1.Footprint

ft
ft

Measure to the outside of the overhangs, not the walls. A 1 ft eave on each side adds 2 ft to both numbers.

2.Pitch

3.Shingles and waste

%

10% suits a simple gable roof. Use 15% or more for hips, valleys and dormers. Check the bundle count and roll coverage on the product you buy.

Shingles to buy

0 bundles

Includes 10% waste

The rest of the list

Material Buy

Drip edge assumes a simple gable: both eaves plus the four sloping rake edges, in 10 ft lengths. Ridge cap, starter strip and flashing depend on the roof's shape, so count those separately.

How roof area is worked out

A roof is always bigger than the ground under it. The steeper it is, the bigger the gap, and that is where most rough estimates go wrong.

  • Footprint = length × width, measured to the outside of the overhangs
  • Pitch multiplier = √(rise² + 12²) ÷ 12
  • Roof area = footprint × pitch multiplier
  • Squares = roof area × (1 + waste) ÷ 100
  • Bundles = squares × bundles per square, rounded up

Roof pitch multipliers

Pitch multiplier and angle for common roof pitches
Pitch Multiplier Angle Notes
2/12 1.014 9.5° Low slope, needs special underlayment
3/12 1.031 14° Low slope, double underlayment
4/12 1.054 18.4° Common on sheds and ranch houses
5/12 1.083 22.6° Common
6/12 1.118 26.6° Very common, walkable
7/12 1.158 30.3° Getting steep underfoot
8/12 1.202 33.7° Roof jacks or staging needed
9/12 1.25 36.9° Steep
10/12 1.302 39.8° Steep
12/12 1.414 45° 45 degrees

Shingles for common buildings

At a 4/12 pitch with 10% waste and 3 bundles to the square.

Roof area, squares and bundles for common building sizes
Building Footprint Roof area Squares Bundles
Shed, 16 × 20 ft 320 sq ft 337 sq ft 3.71 12
Double garage, 20 × 20 ft 400 sq ft 422 sq ft 4.64 14
Garage, 24 × 24 ft 576 sq ft 607 sq ft 6.68 21
Small house, 30 × 30 ft 900 sq ft 949 sq ft 10.44 32
House, 40 × 30 ft 1,200 sq ft 1,265 sq ft 13.91 42
Large house, 50 × 36 ft 1,800 sq ft 1,897 sq ft 20.87 63

Bundles by roof area

For when you already know the roof area, with 10% waste.

Shingle bundles needed by roof area
Roof area Squares 3 bundle shingles 4 bundle shingles
800 sq ft 8.8 27 36
1,000 sq ft 11 33 44
1,200 sq ft 13.2 40 53
1,500 sq ft 16.5 50 66
1,800 sq ft 19.8 60 80
2,400 sq ft 26.4 80 106

Roofing in Canada? Shingles are still sold by the square and the bundle. Switch the calculator to metres and it converts the footprint for you; one square is 9.29 m².

Before you order

  • Count starter strip and ridge cap separately. They are sold by the linear foot or bundle and depend on the length of your eaves and ridges.
  • Low slopes need special treatment. In the US, the 2021 IRC (section R905.2.2) does not allow asphalt shingles below 2/12 and calls for double underlayment from 2/12 up to 4/12. Check the shingle wrapper and your local code, especially in Canada.
  • Ice and water shield is required along the eaves in much of Canada and the northern US. Confirm the width with your local building department.
  • Plan for the tear off. Old shingles are heavy, so book a bin or dumpster sized by your roofer or the rental company for the number of squares coming off.

Common questions

How many bundles of shingles are in a square?
Three bundles make one square (100 sq ft) for most standard asphalt shingles. Heavier architectural and designer shingles can be four or five bundles a square, so check the wrapper. The calculator lets you pick 3, 4 or 5.
How many bundles of shingles do I need for a 24x24 garage?
At a 4/12 pitch with 10% waste, a 24 × 24 ft garage has about 607 sq ft of roof, which is 6.68 squares or 21 bundles of a 3 bundle shingle. Measure to the outside of the overhangs, which adds to the footprint.
How many bundles of shingles for 1,000 square feet?
1,000 sq ft of roof with 10% waste is 11 squares, so 33 bundles of a 3 bundle shingle, or 44 of a 4 bundle one. Make sure the 1,000 is roof area, not the floor area of the house.
What is a roofing square?
A square is 100 square feet of roof surface, about 9.29 m². Shingles, underlayment and roofing quotes are all priced by the square, so a 2,000 sq ft roof is a 20 square roof.
How do I find my roof pitch?
Pitch is how many inches the roof rises for every 12 inches across. Hold a level horizontally against the roof or a rafter, measure 12 in along it, then measure straight up to the roof surface. A 6 in rise is a 6/12 pitch. Many free phone apps also read it from a photo.
How does pitch change the amount of shingles?
A sloped roof has more surface than its footprint. The multiplier is exact geometry: a 4/12 roof is 1.054 times the footprint, a 6/12 is 1.118, and a 12/12 is 1.414, which is 41% more roof than ground.
How many shingles for a 40 by 30 house?
At a 6/12 pitch with 10% waste, a 40 × 30 ft footprint has about 1,342 sq ft of roof, 14.76 squares, so 45 bundles of a 3 bundle shingle and 2 rolls of synthetic underlayment.
How much waste should I allow for shingles?
10% for a simple gable roof, and 15% or more for hip roofs, valleys and dormers, where more shingles get cut. Starter strip and ridge cap are sold separately and are not part of the waste figure.