Gambrel Roof Shingle Calculator: Squares and Bundles
Convert roof area to squares, bundles, and cost, with gambrel-appropriate waste factor.
What a Roofing Square Means
One roofing square equals 100 ft² of roof surface. Every shingle product on the market is sold by the square or by the bundle, with the bundle wrapper printed with coverage in square feet. Order in whole bundles, never partial. Leftovers go on the shelf for repairs.
Waste Factor for Gambrel
A gable roof typically needs 10% waste. A gambrel needs 15% because every shingle course at the knuckle must be cut to fit the pitch change, and the cuts produce scrap. Add another 5% if the roof has dormers, valleys, or skylights. Steep lower slopes (75°) can push waste to 20% because shingles slide and need replacement during install. For the shingle line item alongside rafter lumber and sheathing in one total, use the roof cost calculator.
Bundles per Square by Type
| Shingle Type | Coverage per Bundle | Bundles per Square | Typical Cost per Square |
|---|---|---|---|
| 3-tab asphalt | 33.3 ft² | 3 | $30–$45 |
| Architectural asphalt | 33.3 ft² | 3 | $40–$80 |
| Designer / luxury | 20–25 ft² | 4–5 | $120–$250 |
| Cedar shake | 25 ft² | 4 | $200–$400 |