Roofing Squares and Bundles: How to Order Shingles for Any Roof

What a roofing square measures

A square measures roof surface, not floor area. A house with a 1,472 sq ft footprint (including overhang) has 16.5 squares of roof at 6:12 before any waste, because a sloped surface is larger than the ground under it. An order built from the floor plan alone comes up short.

Three bundles per square is common for standard asphalt shingles. Some heavier and specialty products pack more bundles per square. Read the coverage printed on the wrapper of the product you are buying and replace the 3 in the formula with that number.

From plan area to roof area

Pitch is the rise in inches for every 12 inches of horizontal run. At 6:12 the roof surface travels 13.42 in. for every 12 in. of run, the long side of a 12 by 6 triangle (the square root of 144 + 36). Dividing by 12 gives the pitch factor $\sqrt{1+(\text{rise}/12)^{2}}$, which is 1.1180 at 6:12. Roof surface equals plan area times that factor. The rule holds for any roof shape as long as every plane has the same pitch.

The plan area includes the overhang. The calculator adds the overhang on all four sides: (L + 2 × overhang) × (W + 2 × overhang). Take length and width at the walls, then add what the eaves and rakes project.

Pitch changes the order size. A 2,000 sq ft footprint is 21.1 squares at 4:12 and 28.3 squares at 12:12, about 34 percent more roof under the same floor plan.

Roof shape and waste allowance

At a uniform pitch, a hip roof and a gable roof over the same footprint have the same surface area. What changes is the cutting. Hips, valleys, dormers, and the ends of every ridge produce triangular offcuts that cannot be reused. The calculator covers that with a complexity factor of 1.00 for a simple gable, 1.05 for a hip, and 1.15 for a cut-up roof with valleys.

Complexity and waste multiply. A cut-up roof at the 10 percent default carries a total allowance of 1.15 × 1.10 = 1.265 over the slope area. Treat the result as the full order and do not add a third allowance from a separate waste tool. The material waste guide explains how those allowances are normally set.

The cut-up roof needs 8 more bundles than the simple gable at 10 percent waste, and 66 bundles in total at 15 percent. For an L-shaped, T-shaped, or multi-wing house, split the plan into rectangles, run each wing at its own pitch, and add the results. Dormers with a different pitch get their own line.

Worked example: 44 × 30 ft gable roof

A 44 × 30 ft house with a 12 in. overhang, a 6:12 pitch, and the ridge running along the 44 ft side. The calculator default of 10 percent waste applies.

1. Add the overhang to each side: 12 in. on both ends of each dimension adds 2 ft. The footprint is 46 × 32 = 1,472 sq ft.
2. Pitch factor at 6:12: the square root of 1 + 0.5² = 1.1180.
3. Roof surface: 1,472 × 1.1180 = 1,645.7 sq ft.
4. Add 10 percent: 1,645.7 × 1.10 = 1,810.3 sq ft, which is 18.10 squares.
5. Bundles: 18.10 × 3 = 54.3, rounded up to 55.
6. Underlayment: 1,810.3 ÷ 400 = 4.53, rounded up to 5 rolls.

Cross-check: the roof pitch and rafter calculator with a 30 ft span, a 44 ft length, and a 12 in. overhang returns 1,645.7 sq ft and 55 bundles. Both tools multiply (span + 2 × overhang) by (length + 2 × overhang) by the pitch factor, so a gable roof gives the same answer either way. The roof pitch chart covers the rafter side of the same geometry.

Underlayment, starter, ridge cap, and drip edge

Underlayment. The calculator divides roof area with waste by 400 sq ft, the coverage of a 4-square roll. Roll sizes differ by product, and some synthetic underlayments come in larger rolls. Check whether the label coverage already accounts for the laps. On slopes from 2:12 up to less than 4:12 the IRC calls for double underlayment under asphalt shingles, and it does not allow asphalt shingles below 2:12. The calculator counts a single layer, so double the roll count on those roofs and confirm the rule with your local building department.

Starter strip. The calculator returns the plan perimeter, 156 ft on the example. Manufacturers differ on whether rakes get starter, and eaves alone come to 92 ft. Follow the instructions for the shingle you use.

Drip edge. The IRC requires drip edge at the eaves and rakes of shingle roofs, so the quantity is eave length plus rake length. Rakes run along the slope, so the plan perimeter understates them. On the example, each of the four rake edges is 17.9 ft long (16 ft of run × 1.1180). Eaves plus rakes come to about 164 ft, not 156 ft.

Ridge cap. The calculator returns 46 ft, which is the ridge of a gable roof including the overhang at both ends. A hip roof over the same footprint has a ridge of only 44 − 30 = 14 ft, plus four hips. Each hip runs 15 ft × the square root of (2 + 0.5²) = 22.5 ft, so the cap totals about 104 ft before overhang. Cap coverage per bundle varies by product.

What to check before you order

1. Take length and width at the walls, then add the eave and rake overhang you measure.
2. Read the pitch from the plans, or measure it: hold a level horizontal against a rafter, mark 12 in. along the level, and measure the vertical distance up to the rafter.
3. Split L-shaped and multi-wing plans into rectangles and total them.
4. Confirm bundles per square and ridge cap coverage on the actual product, and whether starter and cap are separate items.
5. Order the whole roof at once and compare the lot numbers on the wrappers. Color can vary between production runs.
6. Round bundles up. A short order delays the job more than a leftover bundle costs.

Common mistakes

• Ordering from the floor plan. Dividing the 44 × 30 ft floor area by 100 gives 13.2 squares and 40 bundles. The roof needs 55. The order is 15 bundles short.
• Leaving out the overhang. With no overhang the same roof computes to 49 bundles, 6 fewer than the 55 above. A 12 in. overhang adds about 11.5 percent to the footprint of this house.
• Applying the pitch factor twice. If your dimensions are already measured along the slope, such as a tape run up the rafter or a measured roof plane, skip the pitch factor.
• Stacking allowances. A cut-up roof at 15 percent waste is already 1.15 × 1.15 = 1.32 times the slope area. A further margin from another calculator compounds it. Pick one source for each allowance.
• Counting one layer of underlayment on a low slope. Roofs between 2:12 and 4:12 need the roll count doubled where double underlayment is required.

Frequently asked questions