How Many Shingles Do I Need?
Work out how many asphalt shingle bundles, roofing squares and underlayment rolls your roof needs. Enter your building footprint, roof pitch and waste allowance, and this calculator uses the standard pitch-factor formula roofers use. Check the result with your supplier before ordering.
Calculate shingles, squares and underlayment
Measure the building footprint in feet, including overhangs. Nothing is saved.
YOUR ROOF — ESTIMATE ONLY, CHECK WITH YOUR SUPPLIER
| What | Result |
|---|---|
| Footprint, including overhang | |
| Pitch factor | |
| Roof surface area | |
| Roofing squares | |
| Shingle bundles to order | |
| Underlayment rolls (#15 felt) | |
| Ridge cap bundles |
One roofing square is 100 square feet. One roll of #15 felt underlayment covers about 4 squares. Ridge cap: about 35 linear feet per bundle — check the wrapper.
How the shingle calculator works
The calculator takes your building footprint, adds the overhang on each side, and multiplies by the pitch factor to get the true sloped roof area. A sloped roof always has more surface than its flat footprint — a 6/12 pitch adds about 12% more area. It then divides by 100 to get roofing squares, adds your waste allowance, and multiplies by 3 bundles per square for standard shingles. The formula is: roof area = footprint × √(1 + (rise ÷ 12)²), and bundles = squares × 3, rounded up.
Infographic: pitch is the rise over a 12-inch run, and the pitch factor turns a flat footprint into the true sloped roof area. Original diagram, not a photo of a completed job.
Roof pitch factors — the table roofers use
Multiply your flat footprint by the pitch factor to get the true roof area. The steeper the roof, the bigger the factor — a 12/12 roof has over 40% more surface than its footprint.
| Pitch | Angle | Pitch factor | What it means |
|---|---|---|---|
| 3/12 | 14.0° | 1.031 | Low slope — 3% more area than the footprint |
| 4/12 | 18.4° | 1.054 | 5% more area |
| 5/12 | 22.6° | 1.083 | 8% more area |
| 6/12 | 26.6° | 1.118 | Common Bellevue pitch — 12% more area |
| 7/12 | 30.3° | 1.158 | 16% more area |
| 8/12 | 33.7° | 1.202 | 20% more area |
| 9/12 | 36.9° | 1.250 | 25% more area |
| 10/12 | 39.8° | 1.302 | 30% more area |
| 12/12 | 45.0° | 1.414 | Steep — 41% more area |
Need shingle repair in Bellevue? Call now for a free inspection and a written quote.
How much waste should you add?
Waste is the shingles lost to cuts. A simple gable roof with two straight slopes wastes the least — 10% is enough. Add 15% for a roof with a few valleys or dormers, and 20% for a complex roof with many hips, valleys and cuts, because every shingle cut at a hip or valley line cannot be reused. If you are only repairing a small area, waste is already covered by the few spare bundles a roofer carries — see our missing shingle repair service and the shingle repair cost estimator for repair prices. For a full re-roof, order the calculator's bundle count and keep two or three spare bundles for future repairs.
Shingle calculator FAQs — Bellevue, WA
How many bundles of shingles are in a roofing square?
Three bundles make one roofing square for standard 3-tab and architectural shingles. A roofing square covers 100 square feet of roof surface, so one bundle covers about 33.3 square feet. Heavy designer shingles can take four or five bundles per square, so always read the wrapper on the bundle you are buying before you order.
Do I need to add extra shingles for waste?
Yes. Add 10% for a simple gable roof, 15% for a roof with a few valleys or dormers, and 20% for a complex roof with many hips, valleys and cuts. Every shingle cut at a hip or valley line cannot be reused, so complex roofs waste more. This calculator adds the waste percentage you pick before it works out the bundles.
What is a roofing square?
A roofing square is 100 square feet of roof surface — the unit roofers measure in. A 2,000 square foot roof is 20 squares. Because a sloped roof has more surface than its flat footprint, the calculator first multiplies your footprint by the pitch factor, then divides by 100 to get the squares.
Does this calculator include ridge cap shingles?
Not unless you enter a ridge length. Ridge cap shingles are sold separately from field shingles, and one bundle covers about 35 linear feet of ridge or hip line. Measure your ridge and hip lines, enter the total length, and the calculator adds the ridge cap bundles. Always check the wrapper — coverage varies by product.
Repairing rather than replacing? Use the cost estimator or call (425) 738-3670 for a free inspection with photos and a written quote.