Quick answer: bundles = plan area × slope factor × (1 + waste) ÷ coverage per bundle, rounded up. At 3 bundles per square, a 1,653 sq ft roof (with waste) needs 50 bundles.
How to calculate roof shingles
- Measure each roof face on plan: length along the eave and level depth from eave to ridge, overhangs included.
- Plan area × slope factor √(1 + (pitch ÷ 12)²) = sloped roof area.
- Add waste, divide by the bundle coverage on the wrapper and round up.
- Starter strip runs along the eaves; drip edge along eaves and rakes; ridge cap along ridges and hips.
Example: a 6/12 gable roof
Two faces, each 42 ft along the eave and 16 ft deep: 42 × 16 × 2 = 1,344 sq ft on plan. × 1.1180 = 1,502.64 sq ft of roof; +10% = 1,652.90 sq ft = 16.53 squares. ÷ 33.3 sq ft per bundle = 49.6, so 50 bundles. Eaves 84 ft of starter strip; with 71.6 ft of rakes, 155.6 ft of drip edge (16 pieces of 10 ft before overlaps); 42 ft of ridge cap.
The slope factor is plain geometry. Bundle coverage and waste are product and roof specific; the calculator does not check minimum slope, underlayment or any building code.
Frequently asked questions
How many bundles of shingles do I need?
Work out the sloped roof area (plan area × slope factor), add waste, and divide by the coverage on the bundle wrapper. Many shingles are packed 3 bundles to a square (100 sq ft), about 33.3 sq ft a bundle, but some are 4 or more, so use your product’s figure.
What is a roofing square?
A square is 100 sq ft of roof surface (about 9.29 m²). Shingle prices and labour are often quoted per square.
How much waste should I add?
Simple gable roofs are often planned with about 10% extra; roofs with hips, valleys and dormers need more, often 15% or so. Starter strip and ridge cap are counted separately here.
How does pitch change the roof area?
A sloped roof has more surface than its plan area. The slope factor is √(1 + (rise ÷ 12)²): 1.118 at 6/12 and 1.414 at 12/12. Multiply the plan area by it.
Does this check minimum pitch or local code?
No. Shingle makers and building codes set minimum slopes and underlayment rules; check them for your roof and area.
Is this roof shingle calculator free to use online?
Yes. The CalcWall Roof Shingle Calculator is completely free and works online in any browser, on a phone, tablet or computer. There is nothing to download and no account to create, and the math runs right in your browser, so results appear as you type.