Key Takeaways
- Standard asphalt shingles are packaged three bundles to the square
- A roofing square is 100 square feet of actual sloped roof area
- Waste allowance covers cuts at hips, valleys, ridges and edges
- Starter strip and ridge cap shingles are bought separately from field bundles
Ordering shingles starts with the same footprint-to-roof-area conversion used for roof square footage, then adds a waste allowance and converts the result into whole bundles, since that is what actually gets purchased.
From footprint to squares
A building’s footprint area, multiplied by the pitch multiplier (the square root of pitch squared plus 144, divided by 12), gives the actual sloped roof area. Dividing by 100 converts that into roofing squares, the unit shingles are priced and packaged by. A 40 by 30 foot footprint at a 6 in 12 pitch works out to about 1,342 square feet of roof, or 13.4 squares.
Waste allowance and bundle count
A roof is rarely a single clean rectangle: hips, valleys, ridges and edges all require cuts, and cut shingles are waste. A 10 percent waste allowance is a reasonable default for a moderately complex roof; a simple gable roof might need less, a roof with many hips and valleys more. Applied to the example above, 13.4 squares becomes about 14.76 squares with waste.
Standard asphalt shingles are packaged three bundles to the square, a near-universal convention across manufacturers, worth confirming on the specific product before ordering. Multiplying 14.76 squares by 3 bundles per square and rounding up gives 45 bundles.
What is not in the bundle count
Starter strip shingles, laid along the eaves to anchor the first course, and ridge cap shingles, laid along the peak, are sold as separate products from field shingle bundles and cover linear footage rather than square footage. Budget for them separately using your roof’s eave and ridge length, not as part of the bundle total above.
Use the roof shingle calculator to work out bundles and cost for your own footprint, pitch and waste allowance. If you just need the underlying roof area without going as far as a shingle order, the roof square footage calculator covers that step alone.