Roofing Calculator
Estimate the squares, bundles and installed cost of a new roof.
What you'll need to order
- architectural shingles
- synthetic underlayment
- ice and water shield
- drip edge
- ridge cap
Prices vary by region and haul distance. Get quotes from at least two local suppliers.
How this calculator works
squares = length × width × pitch multiplier ÷ 100 × 1.10
A roofing square is 100 sq ft. The 10% allowance covers starter course, ridge cap and cut waste — raise it to 15% on a roof with several valleys or dormers.
Worked example
With building length 40 ft, building width 30 ft, roof pitch (rise per 12) 6 in, installed price per square 450 , this calculator returns 14.76 .
Waste allowance
The headline figure includes a 10% allowance for waste and over-ordering. The exact requirement is shown alongside it.
Roofing squares by pitch
Figures below assume building length 40 ft × building width 30 ft × installed price per square 450 . Change any measurement in the calculator to get your own numbers.
| Roof pitch (rise per 12) | Squares to order | Shingle bundles |
|---|---|---|
| 3 in | 13.61 | 40.82 |
| 4 in | 13.91 | 41.74 |
| 6 in | 14.76 | 44.27 |
| 8 in | 15.86 | 47.59 |
| 10 in | 17.18 | 51.55 |
| 12 in | 18.67 | 56.00 |
A 40 × 30 ft footprint. Steeper pitches cover more actual roof area for the same footprint — a 12/12 roof needs about 18% more material than a 4/12.
How many squares for a typical roof?
| Job | Size | Squares to order | Material cost |
|---|---|---|---|
| Garage or small ranch | 24 ft × 24 ft × 4 in × 450 | 6.68 | $2,338 – $4,675 |
| Single-storey ranch house | 50 ft × 28 ft × 4 in × 450 | 16.23 | $5,682 – $11,363 |
| Two-storey colonial | 40 ft × 30 ft × 6 in × 450 | 14.76 | $5,165 – $10,331 |
| Steep-pitch Victorian | 40 ft × 26 ft × 10 in × 450 | 14.89 | $5,212 – $10,424 |
| Large modern home | 60 ft × 40 ft × 6 in × 450 | 29.52 | $10,331 – $20,661 |
Measure the building footprint, not the roof surface — the pitch multiplier converts it for you. Add the area of any dormers and detached sections separately.
Cost range uses $350–$700 per square (100 sq ft) for material only.
What does a new roof cost per square?
Material typically runs $350 to $700 per square (100 sq ft). Installed cost for architectural asphalt shingles, including tear-off of one existing layer, underlayment and disposal. Materials alone are roughly $110 to $180 per square.
What moves the price:
- Number of existing layers to tear off — a second layer can add $100 per square
- Pitch: anything above 8/12 needs staging and slows the crew considerably
- Complexity — valleys, hips, dormers and skylights all add flashing labour
- Material: standing-seam metal runs three to five times asphalt shingle
- Region, and the season you book in
Prices are US averages and move with fuel, season and haul distance. Always get two local quotes before budgeting.
Roofing materials and their coverage
| Type | Bundles per square | Notes |
|---|---|---|
| Three-tab asphalt shingle | 3.00 | Lightest and cheapest, 20–25 year life |
| Architectural asphalt shingle | 3.00 | The residential standard, 30–50 year life |
| Premium designer shingle | 4.00 | Heavier; check the manufacturer bundle count |
| Cedar shake | 5.00 | Sold by the square, coverage varies with exposure |
| Standing-seam metal | 1.00 | Sold by the panel, not the bundle |
Bundle counts assume standard exposure. Always confirm against the coverage printed on the wrapper — it is the figure your supplier will order against.
Roof material questions
How many bundles of shingles are in a square?
Three bundles cover one square, or 100 sq ft, for standard three-tab and most architectural shingles. Heavier designer shingles sometimes need four or five bundles per square.
How much does a new roof cost?
Architectural shingles run $350 to $600 per square installed, so a typical 15 square roof costs $5,000 to $9,000. Metal, tile and slate cost two to five times more.
How much waste should I allow on a roof?
Ten percent on a simple gable, 15% on a roof with valleys, dormers or hips. Waste comes from starter courses, ridge caps and the offcuts at valleys, which cannot be reused.
How do I measure my roof from the ground?
Measure the building footprint, then multiply by the pitch multiplier. A 40 by 30 ft house is 1,200 sq ft of footprint; at a 6/12 pitch the multiplier is 1.118, giving 1,342 sq ft of actual roof.
How long does an asphalt shingle roof last?
Three-tab shingles last 20 to 25 years, architectural shingles 30 to 50. Ventilation matters as much as the shingle: an under-ventilated attic cooks the roof from below and can halve its life.
Is it cheaper to overlay or tear off?
An overlay saves $100 or so per square in tear-off and disposal, but most codes allow only two layers total, and you cannot inspect the deck underneath. Tear-off is usually the better value over the life of the roof.
Does a steeper roof cost more to shingle?
Yes, on two counts. The sloped surface is larger than the footprint, and anything above 7/12 requires staging and fall protection, which adds labour. A 12/12 roof can cost 30% more per square than a 4/12.