Roof area from the ground
Three things give the area of a roof, and none of them is measured on it.
- The footprint. The length and the width of the house, along the outside of its walls.
- The overhangs. How far the roof reaches past the walls, measured level. It is added on every side.
- The pitch. The inches of rise for every 12 in of run. The roof pitch calculator finds it from a level and a tape in the attic.
Worked example. A house 40 × 30 ft with 1 ft overhangs, under a gable roof at 6/12.
- Footprint of the roof: 42 ft × 32 ft = 1,344 sq ft
- Roof area: 1,344 × 1.118 = 1,503 sq ft, or 15.03 squares
- Shingles, with 10% extra: 50 bundles
- Sheathing: 47 sheets of 4 × 8, 52 with the extra
- Drip edge: 155.6 ft of eaves and rakes, 16 pieces of 10 ft
- Ridge: 42 ft
Squares and bundles
Roofing is priced and sold by the square: 100 sq ft of roof. A square of shingles would be too heavy to carry, so it comes in bundles, and IKO says of most shingles that three bundles make a square. Not of all: heavier shingles are packed four or five to a square. The number is on the wrapper, and “Bundles to a square” under “Options” takes yours.
Bundles are counted whole, after the extra is added: 15.03 squares is not 50 bundles until the waste is in.
Waste by roof shape
Shingles are cut at every rake, hip and valley, and the offcuts do not always fit somewhere else. The calculator adds 10% for a gable or a shed roof and 15% for a hip roof or a roof of several planes; the same article gives 10 to 15% as the general range, and says the figure is hard to predict. Type your roofer’s own under “Extra shingles”.
The same footprint under a hip roof has the same area, since every plane is at the same pitch, and more cutting: the example takes 52 bundles as a hip, with a ridge of 10 ft and 96 ft of hips to cap.
Everything else on the list
- Sheathing. The roof area in sheets of 4 × 8 ft, 32 sq ft each. Tick “New sheathing” to put the sheets on your list; a roof that keeps its deck needs none.
- Underlayment. By the roll, and rolls differ by a factor of ten. Type the coverage printed on yours.
- Drip edge. Along the eaves and the rakes: on the example, two eaves of 42 ft and four rakes of 17.89 ft. Counted in pieces of the length you enter.
- Starter strip. The same eaves and rakes, by the length one bundle covers.
- Ridge cap. Along the ridge and the hips, by the length one bundle covers.
- Nails. The maker’s pattern says how many go in a shingle, and the wrapper how many shingles make a square. Enter the nails to a square and the page counts them with the extra.
The page does not supply those coverages. Two listings of one starter strip gave us two different lengths: the wrapper in your hand is the source.
Questions about roofing
How many bundles of shingles for a 1,500 sq ft roof?
Fifteen squares: 45 bundles at three to a square, and 50 with 10% extra. That is 1,500 sq ft of roof, not of house: a 1,500 sq ft house has a larger roof.
How do I measure my roof without climbing on it?
Measure the house on the ground, add the overhangs, and find the pitch in the attic or at a gable end. The footprint times the multiplier of the pitch is the roof.
How many squares is my roof?
Its area in square feet divided by 100. A house 48 × 28 ft with 1 ft overhangs at 6/12 has 1,677 sq ft of roof: 16.77 squares, 56 bundles with the extra.
Does a steeper roof take more shingles?
Yes, by its multiplier: 1.054 at 4/12, 1.202 at 8/12, 1.414 at 12/12, over the same footprint.
Sources
- IKO, How Many Square Feet in a Bundle of Shingles. A square is 100 sq ft of roof area. Most popular shingles are sold so that three bundles cover one square, but not all: read the label. Shingle waste is hard to predict; count on about 10 to 15 percent as a general range. Read on .
Updated . How we calculate. Found a mistake? Tell us.