A roofing calculator turns a few measurements into the material list for a shingle roof. Contruva’s free roofing calculator takes the house length and width, the overhang and the pitch, works out the true sloped roof area, then gives you squares, shingle bundles, synthetic underlayment rolls, starter strip, hip and ridge cap, drip edge pieces and nails, plus a material cost if you enter your supplier’s prices.
Open the free roofing calculator in your browser. No login, no email, nothing to pay.
Open the free toolIt handles gable and hip roofs from the footprint, or you can enter a measured roof area and edge lengths straight from a takeoff or aerial report. It works in feet or metres and needs no login. Below is exactly how every number is calculated, with two worked examples you can check by hand.
How to use the roofing calculator
Footprint mode is for a simple rectangular house: you give length, width, overhang and pitch. Roof area mode is for anything more complicated, where you already have the sloped area and edge lengths.
The roof type changes the edges, not the area. A hip roof has more eave, no rakes and four hips that need cap.
Waste percentage, bundles per square, underlayment roll coverage, starter and ridge cap coverage per bundle, drip edge length, shingles per square and nails per shingle. Take these off the wrapper or data sheet for the product you’re quoting.
Enter your price per bundle, roll and piece. The calculator multiplies them by the whole-unit quantities and totals the material before tax.
In footprint mode, measure the outside of the walls and enter the overhang separately. The calculator adds the overhang to all four sides, so a 40 × 28 ft house with a 1 ft overhang becomes a 42 × 30 ft roof plan.
How the calculator finds roof area
A sloped roof has more surface than the ground it covers. The calculator gets the plan area (length × width, overhangs included), then multiplies it by the pitch multiplier for your slope.
| Step | Formula |
|---|---|
| Roof plan | (length + 2 × overhang) × (width + 2 × overhang) |
| Pitch multiplier | √(1 + (rise ÷ 12)²) |
| Roof area | Roof plan × pitch multiplier |
| Squares | Roof area ÷ 100 sq ft |
| Squares to order | Squares × (1 + waste %) |
The multiplier is pure geometry, so it holds for any brand and any province. A 6/12 roof is 1.118, which means every 100 sq ft of plan has about 112 sq ft of roof on it. An 8/12 is 1.202 and a 12/12 is 1.414. For the full chart from 1/12 to 18/12, or to work out a pitch you measured as an angle, use the roof pitch calculator.
Hip roofs use the same multiplier. When every plane has the same pitch, the sloped area of a hip roof equals the plan area times the multiplier, exactly like a gable. What changes is the length of the edges.
Gable vs hip: eaves, rakes, ridges and hips
Starter, drip edge and cap are bought by the linear foot, so the calculator works out each edge of the roof from the footprint.
| Edge | Gable roof | Hip roof |
|---|---|---|
| Eaves | 2 × long side | Full perimeter: 2 × (long side + short side) |
| Rakes | 4 × half the short side × pitch multiplier | None |
| Ridge | Long side | Long side − short side |
| Hips | None | 4 × half the short side × √(2 + (rise ÷ 12)²) |
The hip formula comes from the hip running diagonally across the plan while it climbs. At 6/12 it works out to exactly 1.5, so each hip on a 30 ft wide roof plan is 15 × 1.5 = 22.5 ft long. The ridge assumes the ridge runs the long way and that all four sides share one pitch.
How each material quantity is worked out
| Material | Formula | Default in the calculator |
|---|---|---|
| Shingles | Squares with waste × bundles per square, rounded up | 3 bundles per square |
| Underlayment | Roof area with waste ÷ roll coverage, rounded up | 1,000 sq ft (10 squares) per roll |
| Starter strip | (Eaves + rakes) ÷ coverage per bundle, rounded up | 120 linear ft per bundle |
| Hip and ridge cap | (Ridges + hips) ÷ coverage per bundle, rounded up | 25 linear ft per bundle |
| Drip edge | (Eaves + rakes) ÷ piece length, rounded up | 10 ft pieces |
| Nails | Squares with waste × shingles per square × nails per shingle | 64 shingles, 4 nails each |
The defaults are real published numbers, but they belong to specific products, so change them to match what you’re installing. Checked November 2026:
- Bundles per square. IKO packs Cambridge architectural shingles at 20 shingles per bundle and 60 per square, which is three bundles. Heavier designer shingles can be four or five bundles per square.
- Nails. GAF’s data sheet for Timberline HDZ lists 64 shingles and 256 nails per square at four nails per shingle, or 384 where six nails are required. Pick “6 (high wind)” when the manufacturer or your local code calls for it.
- Underlayment. GAF FeltBuster synthetic is sold in 4 × 250 ft rolls labelled 10 squares, and the label notes the coverage excludes laps. That’s why the calculator applies your waste percentage to underlayment too.
- Starter. GAF lists Pro-Start at about 120.33 linear feet per bundle once the sheets are split.
- Ridge cap. GAF lists Seal-A-Ridge at 25 linear feet per bundle (four bundles for about 100 feet).
The calculator counts starter along the eaves and the rakes, because that’s where most installers run it. If you only start the eaves, use the eave length from the results and divide by the bundle coverage yourself. Drip edge comes out as whole pieces with no allowance for laps or corners, so add one or two.
Worked example: a gable roof
A 40 × 28 ft house, 1 ft overhang all round, 6/12 pitch, gable roof, 10% waste, with the default products and these prices: $48 a bundle of shingles, $130 a roll of underlayment, $65 a bundle of starter, $85 a bundle of ridge cap and $14 a piece of drip edge.
(40 + 2) × (28 + 2) = 42 × 30 = 1,260 sq ft.
1,260 × 1.118 = 1,408.7 sq ft, or 14.09 squares.
14.09 × 1.10 = 15.50 squares to order.
15.50 × 3 = 46.5, rounded up to 47.
1,549.6 sq ft ÷ 1,000 = 1.55, rounded up to 2.
Each rake is 15 × 1.118 = 16.8 ft, and there are four.
151.1 ft ÷ 120 = 1.26 bundles of starter; 42 ÷ 25 = 1.68 bundles of cap; 151.1 ÷ 10 = 15.1 pieces of drip edge.
15.50 squares × 64 shingles × 4 nails.
| Material | Quantity | Price | Total |
|---|---|---|---|
| Shingles | 47 bundles | $48 | $2,256 |
| Underlayment | 2 rolls | $130 | $260 |
| Starter strip | 2 bundles | $65 | $130 |
| Hip and ridge cap | 2 bundles | $85 | $170 |
| Drip edge | 16 pieces | $14 | $224 |
| Material cost | $3,040 |
Those prices are placeholders to show the math, not a quote. Use what your supplier charges you this month, before tax.
Worked example: the same house with a hip roof
Same 40 × 28 ft house, same overhang and pitch, but hipped on all four sides. Hips mean more cutting, so the waste goes up to 15%.
Same plan, same pitch, same multiplier.
14.09 × 1.15 = 16.20 squares, which is 49 bundles (48.6 rounded up).
The full perimeter of the 42 × 30 ft plan.
Ridge 42 − 30 = 12 ft. Each hip is 15 × 1.5 = 22.5 ft, times four.
102 ft ÷ 25 = 4.08, rounded up to 5.
144 ÷ 10 = 14.4, rounded up.
With the same prices, the hip roof comes to $3,377 in material against $3,040 for the gable: two more bundles of shingles and three more of cap, slightly offset by one less piece of drip edge. That’s before the extra labour a hip takes, which belongs in your labour line, not your waste factor.
Using the roofing calculator in metric
Switch to metric and enter metres. The calculator converts to square feet behind the scenes, because shingles are still sold by the square in Canada, and shows area and lengths back in metres. Coverage fields change too: underlayment in square metres per roll and starter, cap and drip edge in metres.
Example: a 12 × 8 m house with a 0.3 m overhang at 6/12 has a 12.6 × 8.6 m roof plan. Times 1.118, that’s 121.15 m² of roof, or 13.04 squares before waste.
Pitch is always rise per 12 of run, even in metric, because that’s how shingle manufacturers and the codes state it. If your plans give an angle or a ratio like 1:4, convert it with the pitch calculator first.
What the calculator doesn’t cover
- Complex roofs. Footprint mode is a single rectangle with one pitch. For L-shapes, dormers, valleys and mixed pitches, measure each plane, add them up, and use roof area mode with your own edge lengths.
- Ice and water shield, valleys and flashing. Price eave protection, valley lining, step and counter flashing, vents and boots as separate lines.
- Low slopes. The IRC allows asphalt shingles down to 2/12 but requires double underlayment from 2/12 up to 4/12. The National Building Code of Canada table sets 1 in 3 (4/12) for normal application and 1 in 6 (2/12) for low-slope application, which has its own rules. Check the code your municipality has adopted and the shingle maker’s low-slope instructions.
- Tear-off, decking and labour. The calculator is a material list. Disposal, plywood and crew hours are pricing decisions, covered in the roofing estimate guide below.
From material list to a roofing quote
The material list is the start of the price, not the end. For tear-off, disposal, rotten decking, labour per square and how to present the whole thing, read how to write a roofing estimate. Then use the contractor markup calculator to turn total cost into a price that hits your margin.
If roofing is your main trade, Contruva is built for it. See Contruva for roofers: build a quote from your price catalog with the squares and bundles from this calculator, send it for e-signature with a deposit, and track the real cost of materials and crew hours against what you priced. Everything is in one plan, Contruva Pro, at $249.99 CAD a month. Try it free for 7 days, no credit card needed.