How to estimate a roof replacement — the complete contractor's guide

Writing a roof estimate isn't just plugging numbers into a calculator. The math is straightforward — what trips up most contractors (and costs them jobs) is missing a step, underestimating waste, or pricing labor wrong for the pitch. This guide walks you through every step, with the formulas you actually need.

Step 1 — Measure the roof

You need the total square footage of the roof surface (not the floor plan / footprint). Three ways to do this:

• Satellite + AI tracing — fastest, ~2 minutes. Tools like RoofMetric's AI detection click on a roof in satellite view and trace the outline, returning surface area with pitch already factored in.
• On-roof tape measurement — most accurate, slowest. Required for complex Mansards, dormers, gambrels.
• Drone photogrammetry — good for properties where satellite is poor or you want fly-over photos for the customer.

For residential reroofs, AI satellite tracing is accurate to within 2–3% of surveyor-grade measurement — plenty good enough for a competitive bid.

Step 2 — Calculate squares

A "square" in roofing means 100 square feet of roof surface. It's the industry standard pricing unit.

Example: 3,200 sq ft of roof = 32 squares.

Step 3 — Factor in pitch (slope)

Steeper roofs need more material per linear foot of floor area, and more labor. If you measured from a floor plan rather than a sloped surface, you need to multiply by the pitch factor:

Most residential roofs are 4/12 to 8/12. Anything steeper than 8/12 typically commands a 20–35% labor premium because of the safety setup required.

Step 4 — Add waste factor

You buy materials in bundles or rolls; you cut them to fit. Waste is real and varies by roof complexity:

• Simple gable roof: 10% waste
• Hip roof: 12–14% waste (more cuts at corners)
• Complex roof with valleys, dormers: 15–18% waste
• Architectural shingles in scattered pattern: add 2–3% more

Step 5 — Price the materials

You're buying more than just shingles. A complete shingle reroof typically includes:

• Architectural shingles: $100–$150 per square (varies by brand/grade)
• Underlayment (synthetic): $25–$40 per square
• Ice & water shield: $80–$120 per square (used at eaves and valleys, ~6 ft from edge)
• Drip edge: $2–$3 per linear foot of perimeter
• Ridge cap: $35–$55 per linear foot of ridge
• Starter shingles: $35–$55 per linear foot of eaves
• Flashings (chimney, sidewall, vent): $50–$200 each unit
• Vents (ridge, box, soffit): $30–$80 each
• Nails, sealants, misc: $5–$10 per square

Step 6 — Tear-off and disposal

Most reroofs require removing the existing material first. Costs:

• Tear-off labor: $50–$80 per square (single layer); $80–$120 per square (double layer)
• Dumpster: $400–$700 for a 20-yard (sufficient for most residential reroofs)
• Disposal fees: usually included in dumpster price; some markets charge by tonnage above a baseline

Step 7 — Labor for installation

Installation labor varies hugely by region and pitch. Typical ranges (architectural shingles, average complexity):

• Low pitch (under 6/12): $200–$300 per square
• Standard pitch (6/12 to 8/12): $250–$350 per square
• Steep (9/12 to 12/12): $350–$500 per square
• Walkable but 12/12+: $500–$700 per square (rope/harness required)

Add 15–25% for complex hip roofs with multiple valleys or for steep dormers requiring scaffolding.

Step 8 — Add overhead, profit, and contingency

Your subtotal is materials + tear-off + disposal + labor. Then you apply markup:

• Overhead (insurance, vehicles, office, payroll burden): typically 12–18%
• Profit margin (target net): 10–15% for solo contractors, 8–12% for established companies
• Contingency (unforeseen rot, decking replacement): build 1–2 sheets of OSB at $50–$80 each into the estimate, or add a "decking replacement: $80/sheet as needed" line item

Step 9 — Write the estimate

A professional estimate has:

• Your company branding — logo, license number, contact info at the top
• Customer name and project address
• Itemized line items with quantities, units, and per-unit prices (NOT a single lump sum — customers want to see what they're paying for)
• Material specs — brand, grade, color of shingles, underlayment type, etc.
• Scope of work in plain language
• What's NOT included — decking replacement beyond contingency, gutter work, etc.
• Payment terms — deposit %, milestones, final balance
• Warranty — manufacturer (typically 30-50 years) and your workmanship (typically 5-10 years)
• Expiration date — most contractors use 30 days
• Clear call to action — "Reply to accept" or a signature link

Step 10 — Send fast, follow up faster

Speed matters. Studies show contractors who deliver estimates within 24 hours win 2x more bids than those who take 3+ days. If you can deliver a polished, signed-via-link estimate while you're still in the customer's driveway, your close rate goes through the roof.