Roofing Calculator
Calculate roof area in squares and number of shingle bundles for any roof pitch and footprint.
Pitch Factor Reference Table
The pitch factor converts a horizontal footprint to actual sloped roof area. Multiply footprint area × pitch factor to get true roof area.
| Pitch | Angle | Pitch Factor |
|---|---|---|
| Flat / 0:12 | 0° | 1.000 |
| 2:12 | 9.5° | 1.014 |
| 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 |
Frequently Asked Questions
What is a roofing square?
A roofing square is a unit of measurement equal to 100 square feet of roof area. Roofing materials — shingles, underlayment, and metal panels — are sold and priced by the square. A 2,000 sq ft roof is 20 squares.
How many bundles of shingles are in a square?
Standard three-tab asphalt shingles require 3 bundles per square (100 sq ft). Heavier architectural/dimensional shingles may require 3–4 bundles per square. Always check the manufacturer's specifications — the bundle count is printed on the packaging.
What is roof pitch and how does it affect material quantity?
Roof pitch is expressed as rise-over-run: a 4:12 pitch rises 4 inches for every 12 inches of horizontal run. Steeper pitches increase the actual roof area compared to the footprint. A 12:12 (45°) pitch has about 41% more surface area than a flat roof of the same footprint. This calculator adjusts for pitch automatically.
How much waste factor should I use for roofing?
Add 10–15% for waste on a simple gable roof. Add 15–20% for hip roofs, complex roof lines, or roofs with many valleys, dormers, or skylights. Waste comes from cuts around edges, valleys, and penetrations. It's better to order slightly more than to run short mid-job.
How do I measure a roof from the ground?
Measure the footprint of the house (length × width) from the ground. Multiply by the pitch factor for your roof slope to get the actual sloped area. For a simple gable roof, measure the footprint of one side and multiply by 2 for both sides. Add about 1 foot of overhang per side to each dimension.