How many bundles of shingles do I need? Squares, waste and accessories
Measure the roof’s footprint, multiply it by the pitch factor to get the sloped area, add about 10% for cuts and divide by 100 for squares. Most architectural and 3-tab shingles come 3 bundles to a square.
At a 6 in 12 pitch a roof is 1.118 times its footprint: a 30 × 20 ft footprint is 671 sq ft of roof, 7.38 squares with 10% extra, so 23 bundles.
Worked example
Example: a 30 × 20 ft footprint at 6 in 12, with 10% extra and 3 bundles to a square.
This example gives 23 shingle bundles.
- Section 1 (gable): 30 × 20 ft footprint = 600 sq ft × 1.118 = 670.82 sq ft
- 670.82 × (1 + 10/100) ÷ 33.3333 = 22.14 shingle bundles before rounding.
- Underlayment: 737.9 sq ft ÷ 1,000 sq ft a roll (GAF FeltBuster, 10 squares a roll) = 0.74, rounded up.
- Starter strip along the eaves and rakes: 104.72 ft ÷ 120 ft a bundle (GAF Pro-Start) = 0.87, rounded up.
- Drip edge: 104.72 ft ÷ 9.83 ft a piece (10-ft pieces lapped 2 in, as the residential code requires) = 10.65, rounded up.
- Ridge cap over the ridges and hips: 30 ft ÷ 25 ft a bundle (GAF Seal-A-Ridge) = 1.2, rounded up.
- Nails: 7.38 squares × 264 a square (66 shingles a square, 4 nails each, the maker’s standard pattern; 6 in high-wind areas), rounded up to the next hundred.
- Vents: 600 sq ft of attic ÷ 300 = 2 sq ft (288 sq in) of open vent area when intake and exhaust are balanced; ÷ 150 = 576 sq in otherwise (International Residential Code R806.2).
Other calculators for this job
Every step of a roof project: measure, the list, what it costs and the quotes.
Roof pitch multipliers
Multiply the footprint, overhang included, by the pitch factor to get the sloped roof area. The last column applies it to a 30 × 20 ft footprint (600 sq ft).
| Pitch | Angle | Pitch factor | 600 sq ft footprint becomes |
|---|---|---|---|
| 3 in 12 | 14.0° | 1.031 | 618 sq ft |
| 4 in 12 | 18.4° | 1.054 | 632 sq ft |
| 5 in 12 | 22.6° | 1.083 | 650 sq ft |
| 6 in 12 | 26.6° | 1.118 | 671 sq ft |
| 7 in 12 | 30.3° | 1.158 | 695 sq ft |
| 8 in 12 | 33.7° | 1.202 | 721 sq ft |
| 9 in 12 | 36.9° | 1.250 | 750 sq ft |
| 10 in 12 | 39.8° | 1.302 | 781 sq ft |
| 12 in 12 | 45.0° | 1.414 | 849 sq ft |
What changes the order?
Same footprint, different pitch: a steeper roof has more surface to cover. A roof report that already gives the sloped area needs no pitch factor.
| Calculator input | Result from those inputs |
|---|---|
| Pitch rise, in 12: 3 | 21 shingle bundles |
| Pitch rise, in 12: 6 | 23 shingle bundles |
| Pitch rise, in 12: 9 | 25 shingle bundles |
| Pitch rise, in 12: 12 | 29 shingle bundles |
Try your own measurements in the roofing calculator.
Footprint and pitch, or sloped area
Measure the house from above, including the overhang, and find the pitch: the inches the roof rises for every 12 inches across. Multiply by the pitch factor: 1.054 at 4 in 12, 1.118 at 6, 1.202 at 8 and 1.414 at 12. If a roof report already gives the sloped area, use it as it is; applying the pitch again counts the slope twice. Measure from plans or from the ground, not on the roof.
Extra for cuts
Add about 10% for a simple gable roof and 15% or more for hips, valleys and dormers, where more shingles are cut. Divide by 100 for squares, then multiply by the bundles per square printed on the wrapper.
The rest of the list
Underlayment comes in rolls: a 10-square synthetic roll covers 1,000 sq ft before laps. Starter strip and drip edge run along the eaves and rakes; ridge cap runs along the ridges and hips, about 25 ft a bundle for GAF Seal-A-Ridge. Nails go 4 to a shingle, 6 in high-wind areas. The roofing calculator lists all of these from your roof.
Check a roofer’s number
Compare the squares on a quote with your measured squares plus extra. If the quote is well above, ask why: a second layer to tear off, steep sections, extra waste on a cut-up roof, or a measuring report that counts something you did not. Ask whether decking repairs are priced per sheet.