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Roofing Guide & Reference
What is a Roofing Square?
A roofing square equals 100 square feet of roof area. This is the standard unit for measuring and selling roofing materials. One square typically requires 3 bundles of asphalt shingles.
For example, a 2,000 sq ft roof equals 20 squares, requiring approximately 60 bundles of shingles.
Understanding Roof Pitch
Roof pitch is expressed as rise over run (X/12). A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance.
| Pitch | Angle | Multiplier |
|---|---|---|
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 12/12 | 45° | 1.414 |
How to Calculate
- Measure the building's footprint (length × width)
- Multiply by the pitch factor
- Add waste factor (10-15%)
- Divide by 100 for squares
- Multiply squares by bundles per square
Material Coverage
- Shingles: 3-4 bundles per square
- Felt: 1 roll covers 4 squares (15 lb) or 2 squares (30 lb)
- Drip edge: Measure roof perimeter
- Ridge cap: Measure ridge length ÷ bundle coverage
- Nails: 1 coil per 2-3 squares
Frequently Asked Questions
One roofing square equals 100 square feet of roof area. Most roofing materials are sold by the square, with 3 bundles of shingles typically covering one square. This standard measurement helps contractors and homeowners accurately estimate material needs for roofing projects.
Roof pitch is measured as the vertical rise over a 12-inch horizontal run. For example, a 6/12 pitch rises 6 inches for every 12 inches horizontally. You can measure it using a level and tape measure, or use a pitch finder app. Simply place the level horizontally against the roof, measure 12 inches, then measure the vertical distance from the roof to the level's end.
Add 10-15% waste factor for simple roofs with few obstructions. For complex roofs with valleys, hips, dormers, or multiple angles, use 15-20%. This accounts for cutting waste, starter strips, ridge caps, and damaged materials. Professional roofers typically order 10% extra for experienced crews on simple roofs.
Standard 3-tab asphalt shingles require 3 bundles per square (100 sq ft). Architectural shingles may need 4 bundles per square. To calculate: determine your roof's total squares, then multiply by bundles per square. Always round up and include your waste factor. For example, 15 squares × 3 bundles = 45 bundles, plus 10% waste = 50 bundles total.
Besides shingles, you'll need: underlayment (felt or synthetic), drip edge (metal flashing), ridge cap shingles, starter strips, roofing nails (1 coil per 2-3 squares), flashing for valleys and penetrations, pipe boots, and ventilation materials. Don't forget ice & water shield for eaves in cold climates.