Shingle Calculator: How Many Bundles Do I Need?

Shingles are ordered by the square

Shingles are ordered by the square, which is 100 square feet of roof surface. That means sloped roof surface, not floor area. If you only know the footprint, the tool multiplies it by the pitch factor (1.118 at 6/12, 1.414 at 12/12) to get the real sloped area. If you have a measurement report or a contractor's number, switch to roof area and enter it.

Then add waste. Every rake, valley and hip gets cut, and the offcuts are usually too small to use, so nobody orders the exact area. Use 10 percent on a simple two-plane gable and 15 on a hip roof. A cut-up roof with dormers and a couple of valleys can go higher.

Ask each roofer which waste number they used. If one bid says 25 squares and another says 30 on the same house, one of them owes you an explanation.

Most shingles come three bundles to a square

Most asphalt shingles, 3-tab and architectural alike, come three bundles to a square. A 3-tab bundle has about 26 shingles and an architectural bundle about 21 (GAF's Timberline HD data sheet lists 64 pieces and 3 bundles per square).

Thick designer shingles are the exception. GAF's Grand Sequoia data sheet says 5 bundles a square, and some other designer lines run 4. Pick the wrong product and you run short by a third or more halfway through the job. The guides to types of shingles and 3-tab vs architectural explain the differences.

Cedar shakes depend on length and exposure (how much of each shake shows). The Cedar Shake and Shingle Bureau's coverage table puts a five-bundle square of 24-inch shakes at 100 square feet with a 10-inch exposure, but only 85 at 8 1/2 inches and 75 at 7 1/2. The tighter you lay them, the more bundles you need. Shakes need 3/12 at minimum, and the Bureau's exposure table starts at 4/12. The cedar shake roof guide covers the rest.

How much does a bundle of shingles cost?

Architectural shingles run about $35 to $55 a bundle at the big stores, 3-tab around $30 to $40 and designer lines $60 to $100. Your local supply yard may be higher or lower.

Starter and ridge cap are counted by the foot

Starter goes along the eaves and usually up the rakes, so the tool adds those two lengths together. It figures 116 feet per bundle, which is CertainTeed's SwiftStart. GAF's Pro-Start and Owens Corning's Starter Strip Plus come in close to that, a little over or a little under.

Ridge cap covers the ridge and every hip, at 25 feet a bundle (GAF Seal-A-Ridge). Some caps run 20 feet and some 33, so read the wrapper and redo the division if yours is different.

Most shingles take four nails each

Four nails per shingle is standard, and six where wind design or the warranty calls for it. Grand Sequoia is the exception: GAF lists 360 nails a square for 72 pieces, or five a shingle, so the tool uses five for the 5-bundle designer option.

A 1 1/4 inch, 11-gauge galvanized roofing nail runs about 218 to the pound in a one-pound box, and the tool rounds that down to 210 to leave a little slack. Coil nails for a nail gun come 7,200 to a carton.

Underlayment is one roll of synthetic per 10 squares, doubled below 4/12. Drip edge comes in 10-foot sticks, lapped a couple of inches at each joint.

How the math works

• Roof area = footprint × √(1 + (pitch ÷ 12)²), or the area you enter.
• Squares to order = area ÷ 100 × (1 + waste ÷ 100).
• Bundles = squares to order × bundles per square, rounded up. Cedar: bundles per square = 5 × 100 ÷ coverage of five bundles at your exposure.
• Starter bundles = (eaves + rakes) ÷ 116, rounded up. Ridge cap = (ridge + hips) ÷ 25, rounded up.
• Nails = squares to order × shingles per square (78 for 3-tab, 64 architectural, 72 designer), rounded up, × nails per shingle: 4 standard, 5 for the 5-bundle designer (GAF's 360 a square ÷ 72), 6 with high-wind nailing. Pounds = nails ÷ 210.
• Underlayment rolls = squares to order ÷ 10. Drip edge = (eaves + rakes) ÷ 9 ft 10 in, rounded up.

The defaults make a worked example: a 1,500 square foot footprint at 6/12, a plain gable 50 feet long. The area is 1,500 × 1.118, or about 1,677 square feet, which is 16.77 squares. With 10 percent waste you order 18.45 squares. Three bundles a square comes to 55.3, so 56 bundles of architectural.

The eaves are 50 feet a side (100 total) and the four rakes about 16.8 feet each (67 total), so there are 167 feet of edge: two bundles of starter and 17 pieces of drip edge. Fifty feet of ridge takes two bundles of cap. Nails come to 1,181 shingles × 4 = 4,724, about 23 pounds, and underlayment is two rolls.

Switch the product to the 5-bundle designer and the nails rise to 1,329 pieces × 5 = 6,645. To price the job as well as list the materials, run the same numbers through the roof cost calculator.