Roofing Calculator: Squares, Bundles and a Material List
Give it the footprint and the pitch and it returns squares, bundles and the rest of the order. The pitch matters more than people expect, because a 6/12 roof is nearly 12 percent bigger than the ground it sits on, and that difference is exactly one extra pallet on a mid sized house.
When the figures look right, the roofing material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- Building length40 ft
- Building width30 ft
- Roof pitch, rise per 12 in6 /12
- Waste allowance10 %
- Ridge length, 0 if unknown40 ft
Roofing squares needed14.8 squares
| Footprint area | 1,200 sq ft |
|---|---|
| Slope multiplier at 6/12 | 1.12 x |
| Actual roof surface | 1,342 sq ft |
| Squares before waste | 13.4 |
| Squares with 10% waste | 14.8order to this number |
The material list this produces
| Shingles, bundles (3 per square) | 45 |
|---|---|
| Synthetic underlayment, rolls (10 sq each) | 2 |
| Starter strip, linear ft | 168 |
| Ridge cap, linear ft | 40 |
| Drip edge, linear ft | 140 |
| Roofing nails, lb | 33 |
What this calculator assumes
- Footprint times the slope multiplier gives the actual roof surface. A 6/12 roof is 11.8 percent larger than the ground it covers, which is the number most people forget.
- Three bundles per square is standard for both three tab and architectural shingles. Check your brand, a few premium lines run four.
- Synthetic underlayment is figured at 10 squares per roll, starter and ridge cap at one linear foot per foot.
Why the footprint is not the roof
Measure a house from the ground and you get the footprint, the flat rectangle the building covers. The roof is bigger, because it climbs. How much bigger depends entirely on the pitch, and the relationship is not a guess, it is right angle geometry.
Take the rise over a 12 inch run, square it, add 144, take the square root, divide by 12. A 4/12 roof gives 1.054, a 6/12 gives 1.118, a 9/12 gives 1.25, a 12/12 gives 1.414. Multiply the footprint by that number and you have the real surface area.
Skip that step on a 2,000 square foot 8/12 roof and you are 400 square feet short, which is four squares, which is twelve bundles. That is a second trip and a crew standing around.
What a square is, and why nobody sells you one
A roofing square is 100 square feet. It is the unit every roofer quotes in and no supplier ships in. Shingles come in bundles, and three bundles cover one square for almost every three tab and architectural product on the market. A few heavy designer lines take four, so read the wrapper.
Underlayment is sold by the roll and rated in squares, commonly 10 squares for synthetic and 4 for felt. Starter and ridge cap are linear, so they follow the eave and ridge lengths rather than the area.
Waste is not optional
Ten percent is the standard allowance on a simple gable. A hip roof cuts more, because every hip is a diagonal cut down the length of the shingle, so 15 percent is closer. A cut up roof with valleys, dormers and multiple planes can reach 20.
Waste is cheaper than a short order. Leftover bundles go back or go in the garage for the repair in year eight, whereas running out mid tear off means a roof open to the weather.
Questions people ask
How many bundles of shingles are in a square?
This calculator figures three bundles per square: the bundle count on the material list is the squares, waste included, times three and rounded up.
Do I measure the roof or the house?
This calculator takes the building footprint and multiplies it by the slope multiplier for your pitch.
Is this calculator free?
Yes. No account, no email, no watermark, and the material list downloads straight from your browser. Nothing you type is sent anywhere.
Roofing estimate template and Roofing invoice template, free, no signup, PDF Word and Excel.
Common sizes, worked out
The same calculator with the numbers already filled in, one page per size, each ending in its own material list.
More sizes, answered
Each row is this calculator run with those numbers when the page was built. Type the same numbers in above to see every line of the working.
| Example | What it assumes | Roofing squares needed |
|---|---|---|
| 10x12 shed roof | A 10 by 12 foot shed at a 4/12 pitch with ten percent waste. | 1.4 squares |
| 16x20 garage roof | A 16 by 20 foot garage at a 4/12 pitch with ten percent waste. | 3.7 squares |
| 24x30 garage roof | A 24 by 30 foot garage at a 4/12 pitch with ten percent waste. | 8.3 squares |
| 800 sq ft house | An 800 square foot footprint, 40 by 20, at a 6/12 pitch with ten percent waste. | 9.8 squares |
| 900 sq ft house | A 900 square foot footprint, 36 by 25, at a 6/12 pitch with ten percent waste. | 11.1 squares |
| 1,100 sq ft house | A 1,100 square foot footprint, 44 by 25, at a 6/12 pitch with ten percent waste. | 13.5 squares |
| 1,300 sq ft house | A 1,300 square foot footprint, 52 by 25, at a 6/12 pitch with ten percent waste. | 16 squares |
| 1,600 sq ft house | A 1,600 square foot footprint, 40 by 40, at a 6/12 pitch with ten percent waste. | 19.7 squares |
| 2,000 sq ft house | A 2,000 square foot footprint, 50 by 40, at a 6/12 pitch with ten percent waste. | 24.6 squares |
| 2,500 sq ft house | A 2,500 square foot footprint, 50 by 50, at a 6/12 pitch with ten percent waste. | 30.7 squares |
| 2,800 sq ft house | A 2,800 square foot footprint, 70 by 40, at a 6/12 pitch with ten percent waste. | 34.4 squares |
| 3,500 sq ft house | A 3,500 square foot footprint, 70 by 50, at a 6/12 pitch with ten percent waste. | 43 squares |
| 4,000 sq ft house | A 4,000 square foot footprint, 80 by 50, at a 6/12 pitch with ten percent waste. | 49.2 squares |