Roof Replacement Cost Calculator
Turn a house footprint and pitch into roofing squares, then into an itemised re-roof estimate — tear-off, shingles, underlayment and accessories, labour, flashing, decking repairs and contingency — priced with numbers you collect locally rather than a national average.
How to use this calculator
- Measure the footprint from the ground, not the roof: the building’s length and width at the eaves, plus how far the roof overhangs on each side. The slope factor turns that flat area into real roof area, exactly as the roof pitch calculator does.
- Set the pitch. Read it from the attic with a level and tape, or from the plans. Pitch matters twice: it adds area (a 6/12 roof has 12% more surface than its footprint, a 12/12 roof 41%), and steep roofs cost more per square to work on.
- Describe the complexity and height. Hips, valleys and dormers waste shingles and slow the crew; a second storey means more ladder time and staging. The factors are approximate — a bid will price them precisely.
- Replace the placeholder prices. A supplier gives you the shingle price per square (three bundles). For labour, tear-off and the accessory bundle, ask each roofer to itemise the bid per square; the ones who will are usually the ones to hire.
The formula
Roofing is estimated in squares, where one square is 100 sq ft of roof surface. The whole estimate hangs off two square counts:
roof area = (length + 2 × overhang) × (width + 2 × overhang) × slope factor, where slope factor = √(1 + (rise ÷ 12)²)
actual squares = roof area ÷ 100 — used for tear-off and labour
squares to order = actual squares × (1 + waste) — used for materials
| Line | Cost |
|---|---|
| Roofing material | squares to order × price per square |
| Underlayment, ice shield, starter, ridge, nails | squares to order × accessory price per square |
| Tear-off and disposal | layers × actual squares × price per square |
| Installation labour | actual squares × labour rate × complexity factor × height factor |
| Flashing, drip edge, vents, boots | flat amount |
| Decking replacement | sheets × installed price per sheet |
| Permit | flat amount |
| Contingency | subtotal × percentage |
Materials carry the waste allowance because cut-offs at hips, valleys and rakes are bought and thrown away; labour does not, because the crew is paid for the roof that exists. Complexity factors of 1.1 and 1.25 and height factors of 1.1 and 1.2 are planning approximations for how much slower the same crew works on a cut-up or tall roof.
Worked example
A 40 × 30 ft one-storey house with 1 ft overhangs, a 6/12 gable roof, one layer to remove and the placeholder prices in the form:
- Footprint including overhang: 42 × 32 = 1,344 sq ft
- Slope factor for 6/12: √(1 + 0.5²) = 1.1180; roof area 1,344 × 1.1180 = 1,503 sq ft, or 15.03 squares
- With 10% waste: 16.53 squares to order — 50 bundles
- Roofing material: 16.53 × $130 = $2,148.77; accessories 16.53 × $35 = $578.52
- Tear-off, one layer: 15.03 × $100 = $1,502.64; labour 15.03 × $200 = $3,005.28
- Flashing and vents $600.00; decking 4 sheets × $75 = $300.00
- Subtotal $8,135.20; contingency 10% = $813.52; estimated total $8,948.72 — $595.53 per square, or $5.96 per sq ft of roof
Labour and tear-off are $4,507.91 of that, materials $3,627.29 — on a shingle roof the crew costs more than the shingles, which is why quotes vary so much for the same house. Change the pitch to 10/12 and the roof grows to 1,750 sq ft; change to a hip roof with dormers and both waste and labour rise. These are the defaults in the form above; press Calculate and the numbers match.
Material tiers, relative to architectural shingles
| Material | Installed cost, roughly | Notes |
|---|---|---|
| 3-tab shingles | 0.8× | Shortest life, flat look; being phased out by many makers |
| Architectural shingles | 1.0× (baseline) | The default residential choice; 25–30 year warranties |
| Designer / premium shingles | 1.5–2× | Thicker, longer warranties, slate or shake look |
| Standing seam metal | 2.5–4× | 40–60 year life; labour is specialised |
| Concrete or clay tile | 3–5× | Very long life; roof structure must carry the weight |
To price any of these, change the material and labour inputs above — the geometry and the other lines are the same roof.
What moves a roofing quote
- Pitch. Above about 7/12 the crew needs roof jacks or a harness and works slower; above 9/12 expect staging.
- Layers. A second layer doubles the tear-off and disposal line, and many codes forbid roofing over two existing layers.
- Decking. Rotten plywood is found after tear-off; the allowance here is a guess until then. Ask how the bid handles extra sheets.
- Access. A drive the dumpster and delivery truck can reach saves hours of carrying bundles.
- Season. Roofers are busiest after storms and in early autumn; shoulder-season bids are often keener.
For the geometry alone — pitch conversions, rafter length, squares and bundles — use the roof pitch calculator; the shingles guide covers bundle counts and the underlayment guide the accessory quantities behind the per-square accessory price.
Frequently asked questions
How much does it cost to replace a roof per square?
It depends on your region, the material and the roof, which is why this page asks for your local prices rather than quoting one figure. With the placeholder rates in the form, a one-storey 6/12 architectural shingle roof with one layer of tear-off comes to about 600 dollars per square including contingency. Metal or tile roofs multiply the material and labour lines several times. Replace the rates with a supplier quote and two itemised bids for a figure that is actually yours.
How do I work out how many squares my roof is?
Multiply the footprint including overhangs by the slope factor for your pitch, then divide by 100. The slope factor is the square root of one plus the pitch ratio squared: about 1.12 for a 6/12 roof and 1.41 for a 12/12 roof. A 42 by 32 foot footprint at 6/12 is about 15 squares of roof. Add 10 to 20 percent when ordering materials for waste.
Is it cheaper to roof over the old shingles?
It saves the tear-off line, but it hides the decking, adds weight, shortens the life of the new shingles because they follow every bump in the old ones, and many codes allow at most two layers. Most roofers and manufacturers recommend a full tear-off; the saving is usually a small share of the total.
Why do roofing quotes vary so much for the same house?
Labour is the larger half of a shingle roof, and how a company prices tear-off, decking, flashing, ventilation and the waste on a cut-up roof differs widely. Ask every bidder to itemise the same lines this calculator uses, confirm what happens if rotten decking is found, and the gap normally explains itself.
How long does a roof replacement take?
A typical single-family shingle roof is torn off and re-covered in one to three days by a crew of four to six, weather permitting. Steep or complex roofs, two layers of tear-off, extensive decking repair, metal and tile all take longer.
Guides
- What Goes Into the Cost of a New Roof?
- Tear Off the Old Roof or Shingle Over It?
- Metal Roof vs Shingles: Comparing the Real Cost
Related calculators
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