To write a roofing estimate, measure the roof’s footprint, convert it to squares (100 sq ft each) using the pitch factor, add a waste factor for cuts, then list every material, labour, tear-off and disposal line before adding overhead and profit. Finish with clear exclusions, a unit price for rotten decking, and an expiry date.
This guide is roofing-specific: squares, pitch multipliers, starter and ridge, ice and water shield, and how to price the plywood you can’t see yet. If you want the general rules for any trade’s estimate, read how to write a contractor estimate first, then come back for the roof math.
What goes in a roofing estimate
A homeowner comparing three roof quotes is mostly comparing the bottom line. The quote that wins is the one that makes the bottom line easy to trust. That means showing enough detail that they can see you measured, without burying them in nail counts.
- Job details: customer name, address, date, estimate number and how long the price holds.
- Roof summary: total squares, pitch, number of existing layers, and the system you’re installing (brand and product line).
- Scope line items: tear-off, deck inspection, underlayment, eave protection, drip edge, starter, shingles, flashing, vents, ridge cap, clean-up.
- Unit prices for unknowns: price per sheet of replaced decking and per extra layer removed.
- Exclusions: what’s not included, such as chimney rebuilds, skylight replacement, eavestroughs or interior repairs.
- Warranty: the manufacturer warranty and your own workmanship warranty, stated separately.
- Payment terms: deposit, balance due on completion, accepted payment methods and taxes.
How to measure a roof in squares
Roofers buy and price by the square: 100 square feet of roof surface. You can’t get that from the ground plan alone, because a sloped roof has more surface than the footprint under it. The fix is the pitch multiplier.
Step 1: Measure the footprint, including overhangs
Measure each roof plane’s horizontal length and width, eave edge to eave edge, including the overhang. Satellite measurement reports or drone software save a climb, but walk the roof yourself before you commit to a price. Reports miss soft spots, bad flashing and extra layers.
Step 2: Find the pitch
Pitch is the rise in inches for every 12 inches of run. Put a level on the roof, measure 12 inches along it, and measure straight down to the deck. A 6-inch drop is a 6/12 pitch. A pitch gauge app does the same thing.
Step 3: Multiply by the pitch factor
Multiply the footprint by the pitch factor to get the true surface area, then divide by 100 to get squares. The factors below come straight from the geometry (the square root of 1 plus rise over run, squared), so they hold for any roof.
| Pitch | Pitch factor | 2,000 sq ft footprint becomes | Squares |
|---|---|---|---|
| 4/12 | 1.054 | 2,108 sq ft | 21.1 |
| 5/12 | 1.083 | 2,166 sq ft | 21.7 |
| 6/12 | 1.118 | 2,236 sq ft | 22.4 |
| 7/12 | 1.158 | 2,316 sq ft | 23.2 |
| 8/12 | 1.202 | 2,404 sq ft | 24.0 |
| 9/12 | 1.250 | 2,500 sq ft | 25.0 |
| 10/12 | 1.302 | 2,604 sq ft | 26.0 |
| 12/12 | 1.414 | 2,828 sq ft | 28.3 |
Measure each plane separately if the roof has sections at different pitches, such as a low-slope porch roof tied into a steep main roof. Low-slope sections often need a different system entirely, so price them as their own line.
How much waste factor to add
Every cut at a hip, valley, rake or dormer throws away shingle. The waste factor covers it. Rules of thumb vary by crew, and your own job records are the best guide, but most roofers work in a range like this:
| Roof type | Typical waste factor to start from | Why |
|---|---|---|
| Simple gable, few penetrations | 10% | Straight runs, cuts only at the rakes |
| Hip roof | 12% to 15% | Every hip line means angled cuts on both sides |
| Cut-up roof with valleys and dormers | 15% to 20% | Lots of short courses and angled cuts |
After each job, compare bundles ordered with bundles used. Five or six jobs will tell you your crew’s real waste factor better than any rule of thumb.
Starter strip and ridge cap are usually counted separately in linear feet, not inside the waste factor. Don’t double count them.
Build the materials list
Work out each material from the measurements, not from a gut feel. The lengths you need are eaves, rakes, ridges, hips and valleys, plus a count of every pipe, vent and wall that needs flashing.
| Material | Measured in | How to calculate it |
|---|---|---|
| Shingles | Bundles | Squares with waste × bundles per square for that product |
| Starter strip | Linear feet | Eaves plus rakes |
| Ridge and hip cap | Linear feet | Ridge plus hips |
| Underlayment | Rolls | Roof area ÷ the roll’s stated coverage, plus laps |
| Ice and water shield | Rolls | Eaves and valleys, as far up as your local code requires |
| Drip edge | 10 ft pieces | Eaves plus rakes ÷ 10, rounded up |
| Ridge or roof vents | Pieces or linear feet | From your ventilation calculation |
| Flashing and boots | Count | Every pipe, chimney, skylight and sidewall |
| Nails and sealant | Allowance | A fixed amount per square from your own records |
Bundles per square depends on the product. IKO, for example, packages its popular laminated lines at three bundles per square but heavier designer shingles at four or five, so check the data sheet or wrapper for the product you’re quoting before you multiply.
Price labour, tear-off and disposal
Labour is where roofing estimates go wrong, because pitch and access change the hours far more than the square count does. Track your crew’s hours per square by roof type and use those numbers.
- Steepness: steep roofs need more roof jacks, staging and fall protection set-up, and every course goes on slower. Track hours per square separately for walkable and steep roofs.
- Layers: two layers of old shingles take noticeably longer to strip and weigh more at the dump. Price each extra layer per square.
- Access: a tight lot where the bin can’t get near the house means hand-carrying debris. Note it on your site visit.
- Storeys: a three-storey roof needs more staging and lifting than a bungalow.
- Disposal: bin rental plus tipping fees. Get current rates from your local hauler; they change.
Use a loaded labour rate: wages plus payroll costs, workers’ compensation and benefits. Then add overhead and profit on top of your job costs. If markup and margin still trip you up, this guide to pricing a contractor job walks through the difference.
Price the unknowns before you find them
The most common roofing dispute is rotten decking found after tear-off. You can’t see it from the top, so don’t guess. Put a unit price on the estimate and have the customer sign it with everything else.
“Decking: we inspect the full deck after tear-off. Any damaged or rotted sheathing is replaced at $X per 4×8 sheet, supplied and installed. We photograph every sheet before replacing it and confirm the count with you the same day.”
Do the same for any extra layer discovered under the visible one, and for rotted fascia. A unit price turns a surprise into a line item instead of an argument. When the change is bigger than a few sheets, handle it as a written change order before you carry on.
Worked example: a 22-square reroof
Here’s a full estimate built the way described above. All prices are illustrative CAD figures to show the method, not market rates. Plug in your own supplier prices, crew costs and margin.
The roof: a simple gable, 40 × 50 ft footprint including overhangs, 6/12 pitch, one existing layer, two plumbing vents, no chimney.
That’s 22.4 squares of actual roof surface.
Simple gable, so 10%. Round up to 25 squares, or 75 bundles at three per square.
Each rake is 20 ft of run × 1.118 = 22.4 ft, and there are four. Starter and drip edge: 189 lf.
| Line item | Quantity | Unit cost | Cost |
|---|---|---|---|
| Laminated shingles | 75 bundles | $48 | $3,600 |
| Starter strip | 4 bundles | $65 | $260 |
| Ridge cap | 2 bundles | $85 | $170 |
| Synthetic underlayment | 3 rolls | $180 | $540 |
| Ice and water shield at eaves | 2 rolls | $140 | $280 |
| Drip edge | 19 pieces | $14 | $266 |
| Ridge vent | 13 pieces | $30 | $390 |
| Pipe boots, nails, sealant | Allowance | $250 | |
| Materials | $5,756 | ||
| Labour, tear-off and install | 72 crew hours | $45 loaded | $3,240 |
| Bin and tipping fees | 1 bin | $650 | |
| Overhead recovery | 22.4 squares | $50 | $1,120 |
| Total cost | $10,766 | ||
| Price at a 20% net margin | $10,766 ÷ 0.80 | $13,460 |
That works out to about $600 per square before tax. Add HST or GST/PST for your province on the invoice; if you’re unsure how sales tax applies to materials, see do contractors charge HST on materials. The decking line goes underneath as a unit price, not in the total.
The method is the same in USD or any other currency. Only the unit costs change. What matters is that every number traces back to a measurement, so if the customer asks why your price is higher than someone else’s, you can show them.
Send it fast, then follow up
Roof replacements are big decisions, and most homeowners collect two or three quotes. The quote that arrives first and is easiest to approve has a real advantage. Writing it up at the kitchen table that night and emailing a PDF two days later gives that advantage away.
Note pitch, layers, access, flashing and vents. Take photos of problem areas to include in the quote.
Show the squares, the system you’re installing, the decking unit price and the warranty.
Ask if they have questions about the scope, not whether they’ve decided.
Offer to walk through the line items or adjust the shingle line to fit their budget.
In Contruva’s quoting software, roof line items live in your price book, so you can build the estimate on site, send it by text or email, and see when it’s opened. The customer signs on their phone and pays the deposit before you order shingles, and follow-ups go out on schedule until they answer. Storm-season calls get answered and booked for an inspection by the AI receptionist while you’re up on another roof. See how it fits together on the Contruva for roofing page, or read how to follow up without being pushy.