How Many Shingles for a 12x20 Shed Roof?
Roofing squares needed
2.8 squares
A 12 by 20 foot shed at a 4/12 pitch with ten percent waste.
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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 length12 ft
- Building width20 ft
- Roof pitch, rise per 12 in4 /12
- Waste allowance10 %
- Ridge length, 0 if unknown20 ft
Roofing squares needed2.8 squares
| Footprint area | 240 sq ft |
|---|---|
| Slope multiplier at 4/12 | 1.05 x |
| Actual roof surface | 253 sq ft |
| Squares before waste | 2.5 |
| Squares with 10% waste | 2.8order to this number |
The material list this produces
| Shingles, bundles (3 per square) | 9 |
|---|---|
| Synthetic underlayment, rolls (10 sq each) | 1 |
| Starter strip, linear ft | 72 |
| Ridge cap, linear ft | 20 |
| Drip edge, linear ft | 64 |
| Roofing nails, lb | 6 |
Roof pitch compared
Pitch is the number most people guess at, and it is worth more shingles than any other input. Same house, five pitches.
| Roof pitch | Roofing squares needed |
|---|---|
| 4/12 | 2.8 squares |
| 6/12 | 3 squares |
| 8/12 | 3.2 squares |
| 10/12 | 3.4 squares |
| 12/12 | 3.7 squares |
What else matters here
Two hundred and forty square feet of footprint at 4/12 is 253 square feet of roof, 2.8 squares with waste, nine bundles.
That figure is the footprint, and a roof is bigger than its footprint in two ways rather than one. The pitch multiplier handles the slope. What it does not handle is the overhang, which on this building might be a foot at the eaves and six inches at the rakes.
A twelve inch eave overhang on both sides of a twelve foot building adds two feet to the span, which is seventeen percent more roof, and that is far more than the waste allowance. Measure the roof from edge to edge including the overhang and use those numbers, not the wall dimensions. The same applies to the drip edge and the starter strip, which both run the real perimeter.
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 12x20 shed?
About 9 bundles at a 4/12 pitch with ten percent waste, which is 2.8 squares.
Should I include the roof overhang when measuring?
Yes. Measure edge to edge including the eave and rake overhangs. On a small building a one foot overhang can add more than fifteen percent to the roof area.
Does the waste allowance cover the overhang?
No. Waste covers offcuts. An overhang is extra roof and has to be measured, or the order comes up short.
The roofing calculator takes any dimensions you like and hands back the same list.