How to use the roofing material calculator
- Choose imperial or metric units and how you will enter pitch (rise per 12 or degrees).
- Add each roof plane with its footprint (length × horizontal width, or plan area) and its pitch.
- Set a waste allowance and the bundles per square for your shingle product.
- Enter underlayment roll coverage, starter and ridge cap coverage from the product labels, plus eave, rake, ridge and hip lengths.
- Read the sloped area, squares and material counts, then copy or print the list.
Worked example
Two 40 × 15 ft planes at 6/12 pitch, 10% waste
Plan area 1,200 sq ft. Slope factor at 6/12 is √(1 + 0.5²) = 1.118, so the roof area is 1,341.6 sq ft = 13.42 squares, or 14.76 squares with 10% waste. At 3 bundles per square that is 44.3, rounded up to 45 bundles. With 400 sq ft underlayment rolls: 4 rolls. 140 ft of eaves and rakes at 100 ft per starter bundle: 2 bundles. 40 ft of ridge at 30 ft per cap bundle: 2 bundles. Roll and bundle coverages are example values.
How it works
Slope factor = √(1 + (rise ÷ 12)²) (or 1 ÷ cos(angle) for degrees). Sloped area = plan area × slope factor, summed over planes. Metric areas convert at 1 m² = 10.7639 sq ft. Squares = area in sq ft ÷ 100. Bundles = ⌈squares × (1 + waste) × bundles per square⌉. Rolls = ⌈area × (1 + waste) ÷ roll coverage⌉. Starter and ridge bundles = ⌈length × (1 + waste) ÷ coverage per bundle⌉.
Assumptions
- A roofing square is 100 sq ft by trade convention.
- Bundles per square defaults to 3, a common packaging convention for many asphalt shingles. Check your product; some are packed differently.
- Underlayment, starter and ridge cap coverages are example values. Use the figures on your product labels.
- Waste percentage is your own allowance for cuts, valleys and hips.
- Plan measurements should include overhangs.
Frequently asked questions
How do I find the pitch?
Measure how many inches the roof rises over 12 inches of horizontal run (for example 6/12), or use a pitch gauge or phone inclinometer app for degrees. The tool converts either to a slope factor.
How many bundles are in a square?
Many standard asphalt shingles are packaged so that 3 bundles cover one 100 sq ft square, but heavier or architectural products may differ. The wrapper states the coverage; enter it here.
How much waste should I allow?
It depends on roof complexity: simple gable roofs need less than roofs with many valleys, hips and dormers. Ask your supplier or roofer for guidance for your roof.
Can I measure from satellite images?
Aerial measurements give a footprint, which you can enter as plan area. Confirm with on-site measurements before ordering.
Limitations
- Treats each plane as a simple rectangle or area; dormers and complex intersections need separate planes.
- Does not estimate flashing, vents, drip edge, nails or ice and water shield.