Understanding your result
The headline is the number of bundles to put on the order. Under it, the stats show the roof area, the squares before waste, the nails for your pattern and, if you entered a ridge and hip length, the bundles of cap. The breakdown table walks from the footprint to the bundles so you can see which step moved the number: the pitch factor, the waste allowance or the rounding to a whole bundle.
The figure to remember is the squares to order, the roof area with waste divided by 100. Every other quantity on the roof is priced or packed per square: the underlayment rolls, the nails, the labor in a quote and the tear-off fee. If a roofer’s estimate names a different number of squares, the difference is almost always the waste allowance or the overhangs, and the table shows both.
The weight row is there for planning rather than ordering. Sixty-six bundles of architectural shingles weigh close to two and a half tons; that is a boom-truck delivery, not a Saturday of carrying bundles up a ladder.
How we calculate this
The one non-obvious step is the pitch factor. A roof plane is the hypotenuse of a right triangle whose base is the horizontal run and whose height is the rise, so its sloped length is the run times √(1 + (rise ÷ 12)²). Multiplying the whole footprint by that factor gives the sloped area of every plane at once, as long as every plane has the same pitch, which is true of almost every gable and hip roof. The pitch factor table lists the factor for every common pitch, and the roof area calculator handles roofs with two pitches or large dormers.
In metric mode the footprint is entered in metres and the pitch in degrees; the factor is then 1 ÷ cos(angle), which is the same number. Squares are kept as the unit of roofing because bundles are packed to them everywhere.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Bundles per square | 3 | Standard packaging for three-tab and architectural shingles (GAF, Owens Corning, CertainTeed, IKO product data); designer shingles 4 or 5 |
| Shingles per square | 64 architectural, 80 three-tab | Manufacturers’ bundle counts: about 21 to 22 architectural shingles or 26 to 27 three-tab shingles per bundle |
| Nails per shingle | 4, or 6 in high wind | ARMA and manufacturers’ installation instructions; six nails required in designated high-wind regions and for the enhanced wind warranty |
| Waste allowance | 10% gable, 15% hip, 20% cut-up | Estimating practice; the waste guide shows where each figure comes from |
| Overhang | 12 in on all sides | A common eave and rake overhang on US houses; measure yours |
| Cap coverage | 33 linear ft per bundle | Three-tab shingles cut into caps at a 5-in exposure (26 shingles × 3 caps × 5 in); purpose-made cap bundles state their own coverage |
| Bundle weight | 65 lb three-tab, 75 lb architectural, 85 lb heavy | Typical published bundle weights; used only for the planning note |
Assumptions last reviewed October 7, 2026.
The calculator does not model a second pitch on the same roof, the shingles saved by reusing offcuts on a long gable, or the extra starter and cap that go on dormers. It counts shingles, not the whole roof: starter strip, underlayment, ice barrier, drip edge and flashing each have their own calculator in this group. For the measuring method that gets the footprint right without a ladder, read the guide on measuring a roof from the ground.
Two worked examples
A plain gable ranch house
A 50 by 32 foot house with 12-inch overhangs and a 6/12 pitch, architectural shingles at three bundles per square, four nails per shingle, and 52 feet of ridge to cap.
- Footprint with overhangs: 52 × 34 = 1,768 sq ft
- Pitch factor: √(1 + (6 ÷ 12)²) = 1.118
- Roof area: 1,768 × 1.118 = 1,977 sq ft = 19.77 squares
- With 10% waste: 21.74 squares
- Bundles: 21.74 × 3 = 65.2, rounded up to 66 bundles
- Nails: 21.74 × 64 × 4 = 5,568
- Cap: 52 ÷ 33 = 1.58, so 2 bundles
Sixty-six bundles is the order; the leftover from the 66th bundle is the spare you keep for repairs. The nails calculator turns 5,568 nails into one box of coil nails.
A cut-up roof measured from a satellite tool
A roof of 3,100 square feet measured plane by plane, with valleys and two dormers, three-tab shingles, six-nail high-wind pattern, and 120 feet of ridge and hips.
- Roof area as entered: 3,100 sq ft = 31 squares
- With 20% waste for a cut-up roof: 37.2 squares
- Bundles: 37.2 × 3 = 111.6, rounded up to 112 bundles
- Nails: 37.2 × 80 × 6 = 17,856
- Cap: 120 ÷ 33 = 3.64, so 4 bundles
The waste allowance alone is 6.2 squares, almost 19 bundles. On a roof like this it is worth checking the valley and dormer cuts against a plan before trimming the allowance; running out mid-job costs more than two spare bundles.
Where to find your inputs
Building length and width. Measure the outside of the walls at the eave sides and the gable sides. On a house with a bump-out, measure the main rectangle and add the bump-out’s roof as extra area.
Overhang. Stand under the eave and measure horizontally from the wall to the drip edge; 12 to 24 inches is usual. Rake overhangs are often shorter; if they differ, use the eave figure, because the eaves are the long sides.
Pitch. Hold a level horizontally against the underside of a rake board or a rafter in the attic, measure 12 inches along it, then measure straight down to the board. That vertical distance in inches is the pitch. The pitch calculator converts a measurement in degrees or any rise and run.
Ridge and hip length. The ridge of a gable roof is the length of the house plus the rake overhangs. Hips run from each corner to the ridge; on a regular hip roof each is about 1.45 to 1.75 times the horizontal distance from the corner to the ridge (half the house width), depending on the pitch.
Common mistakes
- Using the floor area as the roof area. A 2,000 square foot house under a 6/12 roof has about 2,400 square feet of roofing once overhangs and pitch are included. Always start from the footprint and the pitch.
- Forgetting the overhangs. Twelve inches on every side adds 10 percent to the footprint of a 50 by 32 house; on a small shed it adds much more.
- Taking 10 percent waste for every roof. Hips and valleys turn whole shingles into triangles. A hip roof needs 15 percent, a cut-up roof 20, and skimping means a second delivery charge.
- Assuming three bundles per square for every product. Thick designer shingles are packed four or five to the square. Read the wrapper, or the order will be short by a quarter.
- Nailing four when six are required. High-wind regions, pitches over 21/12 and the enhanced wind warranty all call for six nails. The nails calculator prices the difference, which is small.
- Counting the cap as ordinary shingles. Architectural roofs need purpose-made cap; cut three-tab caps are only for three-tab roofs. The cap calculator handles both.
- Mixing lots. Shingles vary slightly in colour between production runs. Buy every bundle at once, from one lot, and keep the leftover bundle from the same lot for repairs.
Questions people ask
- How many bundles of shingles are in a square?
- Three bundles cover one square (100 square feet) for three-tab shingles and for almost all architectural shingles, which is 33⅓ square feet per bundle. Heavier designer and luxury shingles are packed four or five bundles to the square because each bundle would otherwise be too heavy to carry. The wrapper always states the coverage; the calculator's default is 3.
- How many squares is a 2,000 square foot house?
- It depends on the pitch and the overhangs. A 50 by 40 foot house (2,000 square feet of floor) with 12-inch overhangs has a 52 by 42 foot footprint, 2,184 square feet, and at a 6/12 pitch the roof is 2,184 × 1.118 = 2,442 square feet, or 24.4 squares. At 4/12 it is 23 squares; at 9/12 it is 27.3. Add 10 to 20 percent for waste before buying.
- How much waste should I add for shingles?
- About 10 percent for a simple gable roof, where the only cuts are at the rakes and the ridge; 15 percent for a hip roof, where every course is cut at an angle at each hip; and 20 percent or more for a roof with valleys, dormers and many planes. The calculator sets these from the shape you choose and lets you type your own figure.
- How many nails do I need for a square of shingles?
- Four nails per shingle is the standard pattern, six in high-wind regions or on very steep roofs. Three-tab shingles run about 80 to the square, so 320 or 480 nails; architectural shingles run about 64 to the square, so 256 or 384. The calculator's example roof of 21.7 squares with architectural shingles takes about 5,570 nails at four per shingle.
- How much does a bundle of shingles weigh?
- A bundle of three-tab shingles weighs roughly 60 to 70 pounds, a bundle of standard architectural shingles 70 to 80 pounds, and bundles of designer shingles packed four or five to the square 80 to 100 pounds. The calculator's default roof of 66 bundles is close to 5,000 pounds of shingles, which is why suppliers offer rooftop delivery by boom truck.
- Should I measure the roof or the house?
- Measure the house at ground level and let the calculator do the rest. The roof area is the footprint including overhangs multiplied by the pitch factor, √(1 + (rise ÷ 12)²), so a tape measure around the walls, the overhang depth and the pitch from a level and a ruler on a rake board or in the attic are enough. No one needs to be on the roof to count bundles.