Roofing Calculator: How Many Bundles of Shingles Do I Need?

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To figure how many bundles of shingles you need, find the roof's surface area, divide by 100 to get squares, add 10 to 15 percent for waste, and multiply by the bundles per square on the wrapper. That's 3 for most standard shingles, and it's what our roofing calculator assumes. You can get the roof area from the ground: multiply the house footprint, including overhangs, by the slope factor for your roof pitch.

For example, a 40 × 30 ft house with 1 ft overhangs and a 6/12 roof has about 1,503 sq ft of roof. That's 16.5 squares, or 50 bundles, with 10 percent waste.

How many bundles of shingles do you need?

Enter the house footprint, eave overhang, and roof pitch. We convert the footprint to roof surface.

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Most architectural shingles come 3 bundles per square (100 sq ft); check your bundle label. Starter strip, ridge cap, and valleys need extra material.

How to measure a roof without climbing on it

  1. Measure the house footprint. Measure the length and width of the outside walls in feet.
  2. Measure the eave overhang. Measure from the wall out to the edge of the roof, at the eaves and at the gable ends. The calculator adds the overhang to all four sides.
  3. Find the pitch. Pitch is the vertical rise in inches over 12 inches of horizontal run. In the attic, hold a level against the underside of a rafter, mark 12 inches along the level, and measure straight up from that mark to the rafter. You can also read it off the house plans.
  4. Split up mixed roofs. A porch roof or dormer with a different pitch gets its own calculation. Add the squares together at the end.
  5. Choose a waste percentage. GAF says contractors typically include 10 to 15 percent. Owens Corning's estimating guide adds 10 percent for trim. Use more for hips, valleys, and dormers.

Walking a roof to measure it is a fall risk. Measuring the footprint and pitch from the ground or the attic gets you a solid estimate. Leave anything done on the roof itself to a roofer with the right safety gear.

Roof pitch 6/12 and its slope factorRight triangle under a roof: a level held 12 inches level (the run) and a tape measured 6 inches straight up to the roof (the rise) make a 6/12 pitch. The sloped side is 13.42 inches, so the slope factor is 13.42 divided by 12, or 1.118.ROOF PITCH AND SLOPE FACTORRoof12 in run6 inrise13.42 in slopeSlope factors4/12 pitch1.0546/12 pitch1.1188/12 pitch1.20212/12 pitch1.414Pitch = inches of riseper 12 in of run.Slope length: √(12² + 6²) = √180 = 13.42 inSlope factor: 13.42 ÷ 12 = 1.118Roof surface = flat plan area × slope factor
Pitch is the rise over 12 in of run; on a 6/12 roof the sloped side is 13.42 in, so the slope factor is 13.42 ÷ 12 = 1.118.

The shingle formula

The calculator uses:

  • Footprint with overhang = (length + 2 × overhang) × (width + 2 × overhang)
  • Slope factor = √(1 + (pitch ÷ 12)²)
  • Roof area = footprint × slope factor
  • Squares = roof area ÷ 100 × (1 + waste % ÷ 100)
  • Bundles = squares × 3, rounded up

Why this works: when every roof plane has the same pitch, the sloped surface equals the flat footprint times the slope factor. That's true for a simple gable and for a hip roof, as long as all the planes share one pitch. A roofing square is 100 sq ft.

Worked example (the calculator's default values)

A 40 × 30 ft house, 1 ft eave overhang, 6/12 pitch, and 10 percent waste:

  1. Footprint with overhang: (40 + 2) × (30 + 2) = 42 × 32 = 1,344 sq ft
  2. Slope factor: √(1 + (6 ÷ 12)²) = √1.25 = 1.118
  3. Roof area: 1,344 × 1.118 = 1,503 sq ft
  4. Squares: 1,503 ÷ 100 = 15.03, × 1.10 = 16.5 squares
  5. Bundles: 16.53 × 3 = 49.6, rounded up to 50 bundles

The calculator shows: "You need about 16.5 squares of shingles (50 bundles). Roof surface: 1,503 sq ft at a 6/12 pitch (slope factor 1.118), plus 10% for waste."

Cross-check: measure plane by plane

Owens Corning's estimating method measures each roof plane (including dormers), multiplies length × width for each, and adds them up. You can use it to check the calculator. On the example, if the ridge runs the 42 ft length, each side of the gable is 42 ft long and about 17.9 ft from eave to ridge (16 ft of horizontal run × 1.118). Two planes of 42 × 17.9 ft come to about 1,503 sq ft, the same as the footprint method.

The plane-by-plane method is the one to use when sections have different pitches, since each plane gets its own length and slope. For a single-pitch roof, the footprint method is faster and doesn't require measuring along the slope.

From house footprint to shingle bundlesPlan of a 40 by 30 foot house with a 1 foot roof overhang on every side, 42 by 32 feet or 1,344 square feet. Times the 6/12 slope factor 1.118 that is 1,503 square feet of roof, 16.5 squares with 10 percent waste, or 50 bundles.FROM FOOTPRINT TO BUNDLESridgehouse walls 40 × 30 ft (dashed)42 ft32 ft1 ft overhang on every sidePlan area1,344 sq ft× slope factor1.118 (6/12)= roof surface1,503 sq ftPlan: (40 + 2) × (30 + 2) = 42 × 32 = 1,344 sq ftRoof: 1,344 × 1.118 = 1,503 sq ftSquares: 1,503 ÷ 100 × 1.10 = 16.53 → 16.5 squaresBundles: 16.53 × 3 = 49.6 → 50 bundlesMost architectural shingles: 3 bundles per square. Check your bundle label.
Add the overhang on every side, multiply by the slope factor, add 10% waste, and multiply squares by 3 bundles: 16.5 squares, 50 bundles.

Slope factors by roof pitch

PitchSlope factorRoof area per 1,000 sq ft of footprintNotes
3/121.0311,031 sq ftLow slope: double underlayment (GAF)
4/121.0541,054 sq ft
5/121.0831,083 sq ft
6/121.1181,118 sq ft
7/121.1581,158 sq ft
8/121.2021,202 sq ft
9/121.2501,250 sq ft
10/121.3021,302 sq ft
12/121.4141,414 sq ft

GAF says almost all of its shingles can be installed on slopes as low as 2:12, and that slopes from 2:12 up to 4:12 need a double layer of underlayment. Code text based on the IRC says the same: asphalt shingles only on slopes of 2:12 or more, with double underlayment below 4:12 (section R905.2.2 in Seattle's 2021 residential code, for example).

Bundles per square by shingle type

The calculator assumes 3 bundles per square. GAF says that's the count for typical asphalt shingles, Owens Corning says the same for standard 3-tab shingles, and GAF's Timberline HDZ architectural shingle is packed 3 to the square. GAF also notes that some specialty shingles need up to 5 bundles per square because they're heavier. Here's what the example roof (16.53 squares with waste) would need:

ShingleBundles per squareCoverage per bundleBundles for the example
GAF Timberline HDZ (architectural)3About 33.3 sq ft50
GAF Woodland (designer)425 sq ft67
GAF Grand Sequoia (designer)520 sq ft83

The spec sheets show the difference. Timberline HDZ lists 64 pieces per square at a 5 5/8 in exposure, while the larger Grand Sequoia lists 72 pieces per square at a 5 in exposure. For a 4 or 5 bundle shingle, multiply the calculator's squares by that number and round up. Always go by the bundles per square printed on the wrapper or spec sheet.

Starter strip, ridge cap, and the rest

The calculator counts field shingles only. You'll also need:

  • Starter strip along the eaves and the rakes. One bundle of GAF Pro-Start covers about 120 linear feet.
  • Hip and ridge cap. GAF Seal-A-Ridge covers 100 linear feet per 4 bundles, or 25 ft per bundle.
  • Underlayment, drip edge, flashing, and nails, each figured by the area or the length of edge it covers.

Say the example house has a simple gable roof with the ridge running the 42 ft length. The eaves are 2 × 42 = 84 ft. Each rake runs 16 ft horizontally at a 1.118 slope factor, or about 17.9 ft, so four rakes are 71.6 ft. That's 155.6 ft of starter, or 2 bundles of Pro-Start. The 42 ft ridge takes 2 bundles of Seal-A-Ridge (42 ÷ 25 = 1.7).

Tips and common mistakes

  • Using the footprint without the pitch. For the example, 1,344 sq ft instead of 1,503 sq ft would leave you more than 10 percent short.
  • Forgetting the overhangs. With no overhang, the same house shows 14.8 squares and 45 bundles, 5 fewer than it really needs.
  • Assuming every shingle is 3 bundles per square. Designer shingles can take 4 or 5.
  • Using too little waste on a complex roof. At 15 percent, the example becomes 17.3 squares and 52 bundles.
  • Mixing pitches in one calculation. A low-slope porch roof figured at the main roof's pitch will be overcounted, and a steep dormer undercounted.
  • Going over old shingles without checking. IRC-based codes don't allow a new layer over a roof that already has two or more layers of roof covering (section R908.3.1.1 in Seattle's 2021 residential code, for example), and local rules can be stricter. Ask your building department whether a tear-off is required, since that changes the scope of the job.

Frequently asked questions

How many bundles of shingles are in a square?

For typical asphalt shingles it's 3 bundles per 100 sq ft square, according to GAF. That includes standard 3-tab shingles and architectural shingles such as GAF Timberline HDZ. Some heavier designer shingles take 4 or 5 bundles per square, so check the wrapper.

How many square feet does a bundle of shingles cover?

With 3 bundles per square, each bundle covers about 33.3 sq ft. With 4 bundles per square it's 25 sq ft, and with 5 it's 20 sq ft.

How many bundles of shingles do I need for a 1,500 sq ft house?

It depends on the footprint, overhang, and pitch, not the living area. A single-story 50 × 30 ft house with 1.5 ft overhangs and a 6/12 roof has about 1,955 sq ft of roof, or 21.5 squares and 65 bundles with 10 percent waste. A two-story home of the same living area has a smaller footprint and needs less.

How much waste should I add for shingles?

GAF says contractors typically add 10 to 15 percent, and Owens Corning's estimating guide adds 10 percent for trim. Use the low end for a simple gable roof and the high end for hips, valleys, and dormers.

Can I put shingles on a low-slope roof?

GAF says almost all of its shingles can go on slopes as low as 2:12 when installed per the instructions, and slopes from 2:12 up to 4:12 need a double layer of underlayment. Below 2:12, use a roofing system made for low slopes.

Do I need separate starter and ridge shingles?

Usually, yes. Starter strips go along the eaves and rakes, and ridge cap shingles cover hips and ridges. Neither is included in the field shingle count, so estimate them by linear feet.