How to calculate roof squares
A roof square is 100 sq ft of roof surface. Because the roof slopes, its surface is bigger than the footprint of the house, so you multiply the footprint (with overhangs) by a pitch factor. This roofing calculator does that, then works out shingles or metal panels and the trim.
Roof area = footprint x pitch factor
Squares = roof area / 100
Shingle bundles = squares x (1 + waste %) x 3
Worked example: 2,000 sq ft footprint at 6/12
A 50 x 40 ft footprint is 2,000 sq ft. The 6/12 pitch factor is the square root of 1.25, or 1.118, so the roof is 2,236 sq ft: 22.36 squares. With 10% waste you order 24.6 squares, which is 74 bundles of three-bundle-per-square shingles. A gable roof this size has 100 ft of eaves and 89.4 ft of rakes, so 19 ten-foot pieces of drip edge, and a 50 ft ridge.
Common pitch factors
- 4/12: 1.054
- 6/12: 1.118
- 8/12: 1.202
- 10/12: 1.302
- 12/12: 1.414
Assumptions
- The roof is a simple gable or hip over a rectangle. Split complex roofs into rectangles, or use an aerial measurement report.
- Hip roofs have four equal hips; the ridge is the length minus the width.
- Most architectural shingles are 3 bundles per square. Ridge cap coverage, nail counts and metal screw counts vary by product, so the fields are editable.
Building these for a living? See Bolster for roofing contractors, or how digital takeoff and AutoCost turn measurements into priced estimates.
FAQ
How do you calculate roofing squares?
Multiply the footprint of the house, including overhangs, by the pitch factor for the roof slope, then divide by 100. A 2,000 sq ft footprint at 6/12 is 2,000 x 1.118 = 2,236 sq ft, or 22.36 squares.
What is the pitch factor for a 6/12 roof?
The square root of 1 + (6/12) squared, which is 1.118. Multiply the footprint by 1.118 to get the roof surface area. A 12/12 roof has a factor of 1.414.
How many bundles of shingles are in a square?
Most architectural and 3-tab shingles come 3 bundles to the square. Add waste first: about 10% for a gable roof and 15% for a hip, then multiply the squares by 3.
How much waste should I add for a roof?
Around 10% for a simple gable roof and 15% for a hip roof. Roofs with valleys, dormers and many facets can need 15 to 20%.
How do I estimate a metal roof?
Switch the calculator to metal panels. Panels per side are the ridge length divided by the panel coverage width, and each panel runs from eave to ridge: half the width times the pitch factor. Hip roofs are cut per facet, so use the squares for ordering.
Can I turn this into a roofing estimate?
Yes. Add unit prices here for a material total. In Bolster, AutoCost prices roofing materials and labor with live regional costs, and the estimate becomes an interactive proposal the homeowner can sign and pay a deposit on.
