Roofing Calculator
Measure the roof's footprint and pitch to get the true roof area in squares, the number of shingle bundles, and the ridge cap, underlayment and drip edge to go with them.
Enter the roof footprint and pitch.
On this page
How to use the roofing calculator
- Measure the footprint of the roof from the ground: the length and width of the house plus the overhangs. You don't need to climb up.
- Find the pitch — the rise in inches for every 12 inches of horizontal run. A pitch gauge app or a level and tape measure in the attic will tell you; see roof pitch explained.
- Pick gable or hip. The style changes the ridge, hip and edge lengths. For complex roofs, calculate each section separately.
- Read squares and bundles. Roofing is sold by the square: 100 square feet of roof surface.
How roof area is calculated
Pitch factor = √(1 + (rise ÷ 12)²)
Roof area = footprint length × footprint width × pitch factor
Squares = roof area ÷ 100
Bundles = squares × (1 + waste %) × bundles per square
Worked example: a 40 × 28 ft gable roof at 6/12
- Pitch factor: √(1 + 0.5²) = 1.118
- Roof area: 40 × 28 × 1.118 = 1,252 sq ft = 12.5 squares
- With 10% waste: 13.8 squares × 3 = 42 bundles
- Ridge: 40 ft → 2 bundles of ridge cap at 25 ft per bundle
Pitch factor table
| Pitch | Angle | Multiply footprint by |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 5/12 | 22.6° | 1.083 |
| 6/12 | 26.6° | 1.118 |
| 7/12 | 30.3° | 1.158 |
| 8/12 | 33.7° | 1.202 |
| 9/12 | 36.9° | 1.250 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
Bundles, squares and waste
- Bundles per square: most asphalt shingles come three bundles to a square, but some heavy designer shingles need four or more — the wrapper says.
- Waste: about 10% on a simple gable roof; 15% or more on hip roofs and roofs with valleys, dormers and many cuts.
- Starter and ridge: starter strip runs along the eaves (and often the rakes); ridge cap covers ridges and hips. Coverage per bundle varies a lot by product.
- Underlayment and ice barrier: synthetic underlayment rolls commonly cover about 1,000 sq ft; many codes also require ice barrier along the eaves in cold climates.
Frequently asked questions
How many bundles of shingles for a 2,000 sq ft house?
It depends on the roof, not the floor area. A single-story 2,000 sq ft house with 1 ft overhangs and a 6/12 roof has roughly 2,400–2,500 sq ft of roof — about 24 to 25 squares, or around 80 bundles with 10% waste.
How big is a square of roofing?
100 square feet of roof surface — a 10 × 10 ft area.
Can I measure the roof from the ground?
Yes. Measure the house footprint plus overhangs, and multiply by the pitch factor. That's safer than climbing and accurate enough for ordering on simple roofs.