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.
Switch the site to metric — the control is in the footer — and your inputs, your results and the tables below follow. The formula, the constants, the guidance text and the sources stay in US units on purpose: that is how the standards they come from are written, and restating them would detach each figure from the document you are meant to be able to check it against.
Where these numbers come from
- ICC International Residential Code 2021, R905.2 — asphalt shingle application, including the slope below which shingles may not be used
- NIST Special Publication 811 2008 — the roofing square as 100 square feet
Check the edition. Codes are amended every few years, and the one your inspector works from may not be the one named above.
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 . Each row is a link that fills in the calculator above. Send one and the other end sees the same figures you do.
| 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?
Every row here opens the calculator already filled in. Copy that link and the numbers travel with it.
| 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.