Estimate the roof area, the number of roofing squares and the shingle bundles for a gable, hip or flat roof, with a waste allowance and a cost estimate.
Roofing Material Guidelines
Roofing Terminology:
- Square: 100 square feet of roof area
- Bundle: Typically 1/3 of a square (3 bundles = 1 square)
- Pitch: Roof slope expressed as rise over run (e.g., 6:12)
Common Roof Pitches:
- Low pitch (1:12 to 4:12): May require special underlayment
- Medium pitch (5:12 to 8:12): Most common residential
- Steep pitch (9:12+): More material and labor intensive
Important Tips:
- Always add 10-15% waste for cuts and overlaps
- Hip roofs require more material than gable roofs
- Include ridge cap shingles in your estimate
- Consider underlayment, drip edge, and ventilation
- Steeper pitches require more materials due to increased area
What this roofing calculator does
- Gable Roof: length, width, pitch and waste to the roof area, squares and bundles.
- Hip Roof: the same, with an extra allowance for a hip roof and an estimate of ridge and hip cap length.
- Flat Roof: area with waste, in squares and rolls.
- Cost Estimator: material, labour and tear-off cost per square, plus additional costs.
How it is calculated
Enter the horizontal length and width of the roof. The sloped area is that footprint multiplied by the slope factor for the pitch. The slope factor is √(1 + (rise ÷ 12)²), for example 1.118 for a 6:12 pitch and 1.414 for 12:12. One roofing square is 100 square feet.
Bundles are counted at 3 per square. GAF says that is typical for standard 3-tab and architectural asphalt shingles, though some specialty shingles need 4 or 5 per square, so check your package (GAF: how many bundles of shingles are in a square).
The Hip Roof tab adds a 10% allowance on top of your waste factor. Ridge and hip cap length is worked out for a rectangular hip roof with the same pitch on every side: (length − width) for the ridge plus 2 × width × √(1 + slope factor²) for the four hips.
Worked examples: a 40 ft × 30 ft roof at 6:12 with 10% waste is 1,342 sq ft of roof, or 1,476 sq ft with waste, which is 14.76 squares and 45 bundles. The same footprint as a hip roof is 1,623 sq ft with waste, 49 bundles and about 100 ft of ridge and hip cap. A 30 ft × 20 ft flat roof with 10% waste is 6.6 squares, or 7 rolls at 100 sq ft each. In the Cost tab, 2,000 sq ft with 10% waste is 22 squares, and at $100 material, $150 labour and $50 tear-off per square plus $500 of extras it comes to $7,100.
Things to keep in mind
Complex roofs with dormers, valleys and chimneys need more material than a simple estimate shows. Flat roof rolls are assumed to cover 100 sq ft each, so check the coverage of your product. Working on a roof is dangerous, so consider a professional for measuring and installation. These are planning estimates only. Measure your own project carefully, check product labels and local building codes, and confirm quantities with your supplier or a qualified contractor before you buy.
Frequently asked questions
What does a roof pitch like 6:12 mean?
The roof rises 6 inches for every 12 inches of horizontal run.
What is a roofing square?
A roofing square is 100 square feet of roof area, the unit shingles and labour are usually priced in.
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