Roofing guide
Plan your roofing project
What a roofing square is
Roofers measure roofs in squares. One square covers 100 sq ft of roof surface. Shingles are packed in bundles, and three bundles cover one square for most 3-tab and architectural shingles. Some heavier designer shingles need four or more bundles per square, so check the wrapper.
Why pitch changes the area
A sloped roof has more surface than the flat footprint under it. The pitch factor, √(1 + (rise ÷ 12)²), converts the footprint to the real roof area. A 6/12 roof is about 12% larger than its footprint; a 12/12 roof is about 41% larger.
You can measure the footprint from the ground, including the overhangs, so you never need to climb on the roof to get an estimate.
What a shingle count leaves out
- Starter strip shingles along the eaves and rakes.
- Hip and ridge cap shingles.
- Underlayment, ice and water barrier, drip edge and flashing.
- Nails and vents.
Roof pitch factors
| Pitch | Angle | Pitch factor |
|---|---|---|
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
Common mistakes
- Using the floor area of the house instead of the footprint with overhangs.
- Forgetting the pitch factor on a steep roof.
- Ordering 3 bundles per square for a shingle that needs 4.
- Using 10% waste on a cut-up roof with many hips and valleys.
Frequently asked questions
How many bundles of shingles are in a square?
Three bundles for most 3-tab and architectural shingles. Some heavier premium shingles need four or five bundles per square.
How much waste should I add for shingles?
About 10% for a simple gable roof and around 15% for roofs with hips, valleys and dormers.
What is a 6/12 pitch in degrees?
A 6/12 pitch rises 6 in for every 12 in of run, which is about 26.6 degrees. Its pitch factor is 1.118.
Can I measure a roof from the ground?
Yes. Measure the length and width of the house including the overhangs, find the pitch, and multiply the footprint by the pitch factor.