Roofing Calculator
With footprint area 1600 sq ft, roof pitch 6 /12, waste factor 10 percent, roofing comes to 19.68 squares — roofing squares. It is reached in 6 steps, the last of which is 1967.7398 / 100, and each one is printed on the page with its numbers filled in. The formula is the one published by Asphalt Roofing Manufacturers Association, not an approximation fitted to it.
Roofing squares and shingle bundles from the building footprint and the roof pitch. Applies the pitch multiplier, so it is roof area, not footprint.
Formula and sources checked · How we check
Footprint area 1600 sq ft, Roof pitch 6 /12, Waste factor 10
19.68 squares
Roofing squares for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- Pitch multiplier
sqrt(pow(6, 2) + 144) / 121.118- Actual roof area
1600 * 1.1180341,788.854 sq ft- Area with waste
1788.8544 * (1 + 10 / 100)1,967.74 sq ft- Roofing squares
1967.7398 / 10019.677 squares- Bundles (three per square)
ceil(19.677398 * 3)60 bundles- Underlayment rolls (4 squares each)
ceil(19.677398 / 4)5 rolls
Several at once
A job is rarely one of anything. Work out the first, add it, change the figures and add the next — the list keeps what each line was, and totals them.
Ask about this in the chatCompare: a 4/12 roof against 8/12Roof Pitch Multiplier Chart
Worked example
A 1,600 sq ft footprint under a 6/12 roof is 1,789 sq ft of actual surface — the pitch adds 12%. With 10% waste that is 19.7 squares, so 60 bundles. Quotes given in "squares" always mean the sloped area, never the footprint.
How to work it out yourself
- 1.Measure the building footprint under the roof, not the sloping surface.
- 2.Find the pitch: hold a level out 12 in from the roof and measure down to the surface. That drop is the rise per 12.
- 3.Multiply the footprint by the pitch multiplier — the square root of rise squared plus 144, over 12.
- 4.Add waste: 10% for a plain gable, 15–20% once there are hips, valleys or dormers.
- 5.Divide by 100 for squares, and multiply squares by three for bundles.
Roof pitch multipliers
| Roof pitch (/12) | Roofing squares | Pitch multiplier | Bundles (three per square) |
|---|---|---|---|
| 2 | 17.84 squares | 1.01 | 54 bundles |
| 3 | 18.14 squares | 1.03 | 55 bundles |
| 4 | 18.55 squares | 1.05 | 56 bundles |
| 5 | 19.07 squares | 1.08 | 58 bundles |
| 6 | 19.68 squares | 1.12 | 60 bundles |
| 7 | 20.38 squares | 1.16 | 62 bundles |
| 8 | 21.15 squares | 1.2 | 64 bundles |
| 9 | 22.00 squares | 1.25 | 66 bundles |
| 10 | 22.91 squares | 1.3 | 69 bundles |
| 12 | 24.89 squares | 1.41 | 75 bundles |
Against a 1,600 sq ft footprint with 10% waste. The multiplier alone applies to any footprint.
What does it cost?
Typical price is $100–$200 per square. Architectural asphalt shingles, materials only. Installed pricing including tear-off runs several times this.
| Item | Typical price |
|---|---|
| Three-tab shingles | $90–$130 per square |
| Architectural shingles | $100–$200 per square |
| Synthetic underlayment | $45–$90 per roll |
| Installed, including tear-off | $350–$700 per square |
Price ranges as of 2026. Materials pricing moves — treat these as a sanity check on a quote, not as a quote.
The formula
- Pitch multiplier
sqrt(pow(6, 2) + 144) / 12 - Actual roof area
1600 * 1.118034 - Area with waste
1788.8544 * (1 + 10 / 100) - Roofing squares
1967.7398 / 100 - Bundles (three per square)
ceil(19.677398 * 3) - Underlayment rolls (4 squares each)
ceil(19.677398 / 4)
Source: Asphalt Roofing Manufacturers Association, National Roofing Contractors Association
Questions people actually ask
- What is a roofing square?
- 100 sq ft of roof surface. Shingles are sold in bundles covering a third of a square, so three bundles per square is the standard conversion for architectural shingles.
- Why does pitch change the area?
- A sloped plane is longer than its shadow. The multiplier is the hypotenuse over the run: a 4/12 roof adds 5%, a 6/12 adds 12%, a 12/12 adds 41%. Ignoring it under-orders steep roofs badly.
- How much waste for a complex roof?
- 10% for a plain gable. Hips, valleys and dormers force cuts on the diagonal, pushing real waste to 15–20% — and starter and ridge cap are ordered on top of that, not out of it.
Related
- Square Footage CalculatorSquare footage of a room, wall, border, gable end, ring or triangle from feet-and-inches measurements, with a waste factor and the cost.
- Diagonal & Rafter Length CalculatorHypotenuse of a right triangle in feet and inches — brace lengths, rafter runs, and squaring a layout.
- Siding CalculatorSquares of siding for a house from its wall dimensions, with openings deducted and waste added.
- Slope & Grade CalculatorGrade percentage, angle in degrees, ratio and roof pitch from a rise and a run.
- Fence CalculatorPosts, rails, pickets and concrete for a run of fence at a given post spacing. Sections, posts, rails, pickets and the two bags of concrete each post takes.
Read first
- What a Shingle Roof Costs — Squares, bundles, tear-off and the pitch multiplier that makes a steep roof cost more twice over — once for the area, once for the labour of standing on it.
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