40 × 30 ft footprint, 6/12 pitch, 10% wastage
1,342 sq ft of roof, 1,476 sq ft with wastage, 45 bundles or 15 squares.
Roofing calculator
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Enter the footprint of the roof including the overhang. The pitch multiplier turns that flat area into the sloped roof area. A square is 100 sq ft and takes 3 bundles of standard asphalt shingles. Ridge caps, starter strips and underlayment are extra.
ft
ft
%
10% for a simple gable, 15% for hips and valleys.
Enter the price per square, installed (optional).
Roofing squares
15.0
1,200 sq ft of footprint at 6/12 is 1,342 sq ft of roof. With 10% wastage that is 1,476 sq ft, or 45 bundles of shingles.
- Bundles
- 45
- Roof area
- 1,342 sq ft
- Pitch multiplier
- 1.118
- Area in m²
- 124.6
The same footprint at other pitches
| Pitch | Multiplier | Roof area | Squares with wastage |
|---|---|---|---|
| 3/12 | 1.031 | 1,237 sq ft | 13.7 |
| 4/12 | 1.054 | 1,265 sq ft | 14.0 |
| 6/12 | 1.118 | 1,342 sq ft | 15.0 |
| 8/12 | 1.202 | 1,442 sq ft | 16.0 |
| 10/12 | 1.302 | 1,562 sq ft | 17.3 |
| 12/12 | 1.414 | 1,697 sq ft | 19.0 |
From footprint to roof area
Climbing on a roof to measure it is not necessary. Measure the footprint of the house including the overhang, then multiply by a factor for the slope. A steeper roof has more surface over the same footprint.
Take a 40 × 30 ft footprint, which is 1,200 sq ft. At a 6/12 pitch the multiplier is 1.118, so the roof is about 1,342 sq ft. Adding 10% for cuts gives 1,476 sq ft. That is just under 15 squares, and at 3 bundles a square you buy 45 bundles.
The table shows the same footprint at other pitches. Going from 4/12 to 12/12 adds about a third more roof, which is why steep roofs cost more to cover even before the extra labour.
This counts the main shingles only. Ridge caps, starter strips, underlayment, flashing and drip edge are bought separately, so ask your supplier for those by the length of each edge.
Sources
What this calculator does not account for
- Simple gable roofs; hips and valleys need more wastage.
- Ridge caps, underlayment and flashing are extra.
How this is calculated
Formula: Roof area from the footprint
roof area =length × width × √(1 + (pitch ÷ 12)²)What the symbols mean
- pitchRise in inches for every 12 inches across, such as 6/12.
- √(1 + (pitch ÷ 12)²)The pitch multiplier: 1.118 for a 6/12 roof.
Good to know
- One square is 100 sq ft. Standard shingles come 3 bundles to a square.
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Worked examples
Each example is worked out by the same code as the calculator above.
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<iframe src="/embed/roofing-calculator" title="Roofing calculator" width="100%" height="720" style="border:0;max-width:42rem" loading="lazy"></iframe>Questions
What is a roofing square?
100 square feet of roof. Shingles, labour and quotes are usually priced per square.
How many bundles of shingles in a square?
Three for standard three-tab and most architectural shingles. Some heavy shingles need four.
How do I find my roof pitch?
Measure how many inches the roof rises over 12 inches across. A rise of 6 inches is a 6/12 pitch.
How much wastage should I add?
About 10% for a simple gable roof and 15% for a roof with hips and valleys.
Can I measure the roof from the ground?
Yes. Measure the house footprint with the overhang and use the pitch multiplier, as this tool does.