Roof Shingle Calculator Formula
Understand the math behind the roof shingle calculator. Each variable explained with a worked example.
Formulas Used
Roofing Squares
squares = adjusted_area / 100Bundles (3 per square)
bundles = ceil(adjusted_area / 100 * 3)Ridge Cap Bundles (35 ft/bundle)
ridge_bundles = ceil(ridge_length / 35)Underlayment Rolls (4 sq ft/roll)
underlayment_rolls = ceil(adjusted_area / 400)Variables
| Variable | Description | Default |
|---|---|---|
roof_area | Roof Area(sq ft) | 2000 |
waste_percent | Waste Factor(%) | 10 |
ridge_length | Ridge/Hip Length(feet) | 40 |
adjusted_area | Derived value= roof_area * (1 + waste_percent / 100) | calculated |
How It Works
How to Calculate Roof Shingles
Formula
Squares = Roof Area / 100
Bundles = Squares × 3
A "square" of roofing is 100 square feet. Most asphalt shingles come 3 bundles per square. For ridge caps, one bundle covers approximately 35 linear feet of ridge or hip. Always add 10-15% for waste and starter strips.
Worked Example
A roof with 2,000 sq ft of area, 10% waste, and 40 ft of ridge line.
roof_area = 2000waste_percent = 10ridge_length = 40
- 01Adjusted area = 2,000 × 1.10 = 2,200 sq ft
- 02Squares = 2,200 / 100 = 22 squares
- 03Bundles = 22 × 3 = 66 bundles
- 04Ridge cap bundles = 40 / 35 = 1.14 → 2 bundles
- 05Underlayment rolls = 2,200 / 400 = 5.5 → 6 rolls
Ready to run the numbers?
Open Roof Shingle Calculator