Roofing Materials Calculator
Squares, shingle bundles, underlayment and drip edge for a gable or hip roof, with waste included.
Step 1 · Roof size
Enter the footprint, or a roof area you already know.
Units
ftm
ftm
Measure to the edge of the overhangs, not the walls.
sq ftm²
ftm
Step 2 · Roof details
Used for roof area, underlayment layers and drip edge.
Step 3 · Materials
Waste allowance and underlayment roll size.
Quantities rounded up to whole packages. Check bundle coverage on your product’s wrapper.
- Roof squares
- 14.8
- 1,476 sq ft incl. waste
- Bundles
- 45
- 3 per square
- Underlayment
- 2
- rolls · 10 sq each
- Drip edge
- 15
- 10 ft pieces · 147 ft
40 × 30 ft footprint = 1,200 sq ft × 1.118 (6/12) = 1,342 sq ft × 1.10 waste = 1,476 sq ft
Results link:
Materials list
Gable roof · 40 × 30 ft · 6/12 · 10% wasteQuantities rounded up to whole packages. Starter strip, ridge cap, flashing and fasteners are not included. Check bundle coverage on your product’s wrapper.
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How the quantities are calculated
Footprint area is multiplied by the pitch’s rafter multiplier to get the true roof area, then by the waste factor. One square covers 100 sq ft, and standard asphalt shingles come three bundles to a square. Every quantity is rounded up to a whole package.
roof area = length × width × √(1 + (pitch ÷ 12)²)
order area = roof area × (1 + waste %)
squares = order area ÷ 100
bundles = ⌈squares × 3⌉
underlayment rolls = ⌈order area × layers ÷ roll coverage⌉
drip edge pieces = ⌈(eaves + rakes) ÷ 9.83 ft⌉
order area = roof area × (1 + waste %)
squares = order area ÷ 100
bundles = ⌈squares × 3⌉
underlayment rolls = ⌈order area × layers ÷ roll coverage⌉
drip edge pieces = ⌈(eaves + rakes) ÷ 9.83 ft⌉
Assumptions
| Item | Assumption |
|---|---|
| Roof planes | Every plane has the same pitch. Mixed pitches: calculate each section separately. |
| Shingles | 3 bundles per square (100 sq ft). |
| Waste | Your choice of 5–20%. Typical: 10% gable, 15% hip. |
| Underlayment | Nominal roll coverage: synthetic 10 squares, #15 felt 4 squares, #30 felt 2 squares. Two layers from 2/12 to under 4/12. |
| Drip edge | 10 ft pieces lapped 2″. Gable: 2 eaves + 4 rakes. Hip: eaves on all four sides. |
| Not included | Starter strip, ridge cap, valley and step flashing, vents, nails. |
Worked example
A 40 × 30 ft gable roof (measured to the overhangs) at 6/12 with 10% waste and synthetic underlayment:
roof area = 1,200 × 1.118 = 1,341.6 sq ft
order area = 1,341.6 × 1.10 = 1,475.8 sq ft
squares = 14.8 · bundles = ⌈44.3⌉ = 45
underlayment = ⌈1,475.8 ÷ 1,000⌉ = 2 rolls
drip edge = 2 × 40 + 4 × 15 × 1.118 = 147.1 ft → 15 pieces
order area = 1,341.6 × 1.10 = 1,475.8 sq ft
squares = 14.8 · bundles = ⌈44.3⌉ = 45
underlayment = ⌈1,475.8 ÷ 1,000⌉ = 2 rolls
drip edge = 2 × 40 + 4 × 15 × 1.118 = 147.1 ft → 15 pieces
Frequently asked questions
How many bundles of shingles are in a square?
Most asphalt shingles are packed three bundles to a square, and a square covers 100 sq ft of roof. Some heavier designer shingles use four or five bundles per square, so check the coverage printed on the wrapper.
How much waste should I add?
A common rule of thumb is about 10% for a simple gable roof and about 15% for a hip roof or one with valleys, dormers and other cuts. Complex roofs can need more. Starter strip and ridge cap are usually ordered separately.
Why does pitch change how many shingles I need?
A sloped roof is larger than the floor area underneath it. The rafter multiplier converts the flat footprint into true roof area: a 6/12 roof is about 11.8% larger than its footprint and a 12/12 roof about 41.4% larger.
When do I need two layers of underlayment?
Under the International Residential Code, asphalt shingles on slopes from 2/12 up to (but not including) 4/12 need two layers of underlayment. Below 2/12, asphalt shingles are not permitted. The calculator doubles the roll count automatically in that range.
How is drip edge counted?
Drip edge runs along the eaves and the rakes (the sloped gable edges). Pieces are 10 ft long and adjacent pieces must overlap at least 2 inches, so each piece covers about 9 ft 10 in. On a hip roof every edge is an eave.
Sources
- International Code Council, International Residential Code, Sections R905.1.1 (underlayment), R905.2.2 (slope) and R905.2.8.5 (drip edge).
- National Roofing Contractors Association, The NRCA Roofing Manual: Steep-slope Roof Systems.
- Manufacturer installation instructions and package coverage for the product you buy.
Testing
Formulas are shown on this page, based on the cited sources, and covered by automated tests. Methodology