The math behind your estimate
The inputs, allowance, and rounding stay visible.
- Surface
- Roof surface area = Plan area × pitch multiplier (or your known area)
- Squares
- Squares = Roof surface area ÷ 100 ft²
- Bundles
- Bundles = Surface × (1 + waste %) ÷ coverage per bundle, rounded up
Assumptions
- Bundle coverage is taken from your input. Three bundles per square (33.3 ft² each) is the common case for architectural asphalt shingles, but designer, specialty and metal profiles vary widely — the wrapper is authoritative.Source: Typical asphalt shingle bundle coverage
- The field-shingle count does not include starter strip, hip and ridge cap, underlayment, drip edge or fasteners. Those are ordered separately by linear foot or by roll.
- The waste allowance covers cuts at rakes, valleys and penetrations. Simple gable roofs sit near 10%; roofs with multiple valleys and dormers routinely need 15–20%.
- In 'from known roof area' mode the pitch is not applied — enter the sloped surface area, not the footprint, or the order will be short.
Scope note
Material quantities only. This tool does not assess deck condition, structural capacity, layer limits or code requirements — the number of shingle layers a roof may carry and the underlayment required are set by local code.
Frequently asked questions
- How many bundles of shingles do I need for a 1,500 ft² roof?
- 1,500 ft² is 15 squares. With 10% waste that is 1,650 ft², and at 33.3 ft² per bundle you should order 50 bundles. Check the wrapper — if your shingle covers a different area per bundle, the count changes.
- How many bundles are in a square of shingles?
- Three bundles per square is standard for architectural asphalt shingles, giving 33.3 ft² per bundle. Heavier designer shingles can run four or even five bundles per square, so always confirm before ordering.
- Do I order shingles by footprint or roof area?
- Always by roof surface area. A 4/12 pitch makes the roof about 5% larger than the footprint and a 12/12 pitch makes it 41% larger. Use the dimensions mode here and the pitch multiplier is applied for you.
- How much waste should I allow for shingles?
- Around 10% on a simple gable roof, rising to 15% with hips and valleys and up to 20% on a complex roof with several dormers. Valleys are the main driver: every course meeting a valley gets cut at an angle.
Sources
- Asphalt shingle bundle/square coverage conventions
- Standard roof pitch multiplier table