Roofing Squares Explained: Estimating Shingles and Underlayment
Roofers talk in squares, not square feet. Once you know that one square equals 100 square feet, estimating shingles and underlayment becomes straightforward.
A roofing square is simply 100 square feet of roof surface. Shingles and underlayment are sold and estimated by the square, so the first job is to measure your roof area, convert it to squares, and add waste. Safety first: measuring from the ground or from plans is far safer than climbing a steep roof.
Measuring roof area
Measure the footprint of the house, then account for the roof pitch, which makes the actual surface larger than the footprint. Multiply the flat area by a pitch factor: a common 6/12 pitch uses about 1.12, while a steep 12/12 pitch uses about 1.41. A 1,600 square foot footprint at 6/12 becomes about 1,792 square feet, or 17.9 squares.
Pitch multiplier reference
| Pitch | Multiplier |
|---|---|
| 4/12 | 1.054 |
| 6/12 | 1.118 |
| 8/12 | 1.202 |
| 12/12 | 1.414 |
Estimating shingle bundles
Most architectural shingles come three bundles to the square. For 17.9 squares, round up to 18 squares and multiply by 3 to get 54 bundles. Add about 10 percent for waste, ridge caps, and starter courses, which brings the order closer to 60 bundles. Hips and valleys increase waste, so lean toward the higher end.
Underlayment and accessories
Synthetic underlayment typically covers about 10 squares per roll, so 18 squares needs about 2 rolls plus a spare. Add ice-and-water shield along eaves and valleys in cold climates, drip edge along all edges, and enough roofing nails, ridge cap, and starter strip. Each of these has its own coverage figure to plan from.
Waste factors that matter
Simple gable roofs waste the least. Roofs with many hips, valleys, dormers, and penetrations waste more because of the extra cuts and overlaps. Bump your waste allowance from 10 percent up to 15 percent for complex roofs so you are not short during the job.
When to call a pro
Roofing is dangerous and time-sensitive once the old covering is off. Steep pitches, multiple stories, and complex rooflines are jobs for experienced crews with fall protection. Use your estimate to check a contractor's material quote and understand what you are paying for.
Estimating checklist
- Convert roof area to squares (area divided by 100).
- Apply the pitch multiplier for true surface area.
- Add 10 to 15 percent waste based on roof complexity.
- Include underlayment, drip edge, ridge cap, and fasteners.