How Many Shingles for a 20x20 Garage Roof?
Roofing squares needed
4.6 squares
A 20 by 20 foot garage at a 4/12 pitch with ten percent waste.
It does not stop at a number.
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.
How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Building length20 ft
- Building width20 ft
- Roof pitch, rise per 12 in4 /12
- Waste allowance10 %
- Ridge length, 0 if unknown20 ft
Roofing squares needed4.6 squares
| Footprint area | 400 sq ft |
|---|---|
| Slope multiplier at 4/12 | 1.05 x |
| Actual roof surface | 422 sq ft |
| Squares before waste | 4.2 |
| Squares with 10% waste | 4.6order to this number |
The material list this produces
| Shingles, bundles (3 per square) | 14 |
|---|---|
| Synthetic underlayment, rolls (10 sq each) | 1 |
| Starter strip, linear ft | 96 |
| Ridge cap, linear ft | 20 |
| Drip edge, linear ft | 80 |
| Roofing nails, lb | 10 |
Roof pitch compared
Same house, five pitches.
| Roof pitch | Roofing squares needed |
|---|---|
| 4/12 | 4.6 squares |
| 6/12 | 4.9 squares |
| 8/12 | 5.3 squares |
| 10/12 | 5.7 squares |
| 12/12 | 6.2 squares |
What else matters here
Four hundred square feet of footprint at 4/12 is 422 square feet of roof, 4.6 squares with waste, fourteen bundles.
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.
Questions people ask
How many bundles of shingles for a 20x20 garage?
About 14 bundles at a 4/12 pitch with ten percent waste, which is 4.6 squares.
Different numbers?
The roofing calculator takes any dimensions you like and hands back the same list.
Other common sizes
12x16 shed roof2.2 squares12x20 shed roof2.8 squares20x24 garage roof5.6 squares24x24 garage roof6.7 squares1,000 sq ft house12.3 squares1,200 sq ft house14.8 squares30x40 pole barn roof13.9 squares1,400 sq ft house17.2 squares1,500 sq ft house18.4 squares36x48 pole barn roof20 squares1,800 sq ft house22.1 squares2,200 sq ft house27.1 squares2,400 sq ft house29.5 squares3,000 sq ft house36.9 squares40x80 pole barn roof37.1 squares5,000 sq ft house61.5 squares