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Roofing Calculator: Squares, Bundles and Cost
Estimate your roof's real surface area from the house footprint and roof pitch, then see how many squares and bundles of shingles, rolls of underlayment and feet of ridge cap and drip edge you need.
How to measure a roof from the ground
You don't need to climb on the roof. Measure the length and width of the house, add the overhang on each side (often 1 to 2 ft), and multiply. That is the roof's footprint. Then multiply by the pitch factor, which accounts for the slope: a steeper roof has more surface over the same footprint.
| Pitch | Angle | Pitch factor |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 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 |
Example: a 40 × 30 ft footprint with a 6/12 pitch is 1,200 × 1.118 = 1,342 sq ft, or 13.4 squares. With 10% waste for a gable roof, that is 14.8 squares, or 45 bundles of shingles.
What is a roofing square?
Roofers measure in squares: one square is 100 sq ft of roof. Most asphalt shingles (3-tab and architectural) come 3 bundles to a square. Some heavy designer shingles need 4 or 5 bundles, so check the wrapper.
How much waste to add
Use about 10% for a simple gable roof and 15% for a hip roof or one with valleys, dormers and many cuts. Our hip setting uses 15%. Starter strip shingles along the eaves are extra, or you can cut them from regular shingles.
Other materials
- Underlayment: a roll of synthetic underlayment usually covers 10 squares; #15 felt covers about 4 squares.
- Ridge cap: about 30 linear ft per bundle, depending on the product.
- Drip edge: sold in 10 ft lengths for all eaves and rakes.
- Nails: about 320 per square at 4 nails per shingle; use 6 per shingle in high-wind areas.
Asphalt shingle roofs commonly cost $4 to $8 per sq ft installed ($400 to $800 a square), including tear-off of one old layer. Prices vary a lot by region, roof steepness and access.
Frequently asked questions
How many bundles of shingles do I need?
Three bundles per square (100 sq ft) for most asphalt shingles, plus 10 to 15% for waste. A 2,000 sq ft roof is 20 squares, or about 66 bundles with 10% waste.
How do I calculate roof area from the ground?
Multiply the house's length and width including overhangs, then multiply by the pitch factor: 1.054 for 4/12, 1.118 for 6/12, 1.202 for 8/12.