Shingle Calculator — Bundles, Squares & Underlayment
Estimate how many bundles of shingles you need from your roof footprint and pitch. The calculator converts plan area to true roof area, adds cutting waste, and includes underlayment and ridge coverage.
How the shingle estimate works
- 1Plan area = footprint length × footprint width
- 2Roof area: plan area ÷ cos(pitch angle) — a 35° pitch multiplies area by 1.22
- 3Convert to squares: 1 square = 100 sq ft (9.29 m²)
- 4Bundles: typically 3 bundles per square for three-tab, up to 4 for architectural shingles
- 5Apply 10% waste for cuts at hips, valleys, ridges and edges
- 6Underlayment: roof area plus overlaps
Worked example
Gable roof: 10 m × 8 m plan (≈ 33 × 26 ft), 35° pitch.
Roof area: 80 m² ÷ cos(35°) = 97.6 m² ≈ 10.5 squares. With 10% waste: ~11.6 squares → approximately 35 bundles of three-tab shingles, plus underlayment for 115 m².
Frequently asked questions
How many bundles of shingles are in a square?
Most three-tab shingles cover one square (100 sq ft) per 3 bundles; heavier architectural shingles may need 4 bundles per square. Check the product wrapper for exact coverage.
How do I calculate my roof area from the ground?
Measure the building footprint and multiply by the pitch factor: flat = 1.0, 25° = 1.10, 35° = 1.22, 45° = 1.41. That gives the true sloped area.
How much waste should I add for shingles?
Add about 10% for straight gable roofs. Complex roofs with hips, valleys and dormers can need 15% — every cut edge wastes material.
Do I need underlayment under shingles?
Yes — an underlayment membrane is required under shingles in most building codes as a secondary line of defence against wind-driven rain.