Shingle Calculator – Understand Squares, Bundles & Pitch (Fast)
Use this shingle calculator to turn roof measurements into a clear shopping list. It converts your footprint into sloped roof area using the roof pitch factor, subtracts openings, applies a waste allowance, and returns both roofing squares (100 ft² units) and total bundles of shingles. Whether you’re ordering for a garage or a full re-roof, it answers the key question: “How many shingle bundles do I need?”
How the Shingle Calculator Works (Formulas)
- Plan area with overhangs:
(Length + 2 × rake) × (Width + 2 × eave) - Pitch factor:
√(rise² + 12²) / 12(for “rise per 12” pitch) - Sloped area:
plan area × pitch factor − openings - Waste applied:
sloped area × (1 + waste%)(e.g., 10–15%) - Squares:
area_ft² ÷ 100(1 square = 100 ft² ≈ 9.2903 m²) - Bundles:
ceil(area_ft² ÷ bundle coverage)(default 33.3 ft²/bundle)
Common Pitch Factors (quick reference)
4:12 → 1.054 · 6:12 → 1.118 · 8:12 → 1.202 · 10:12 → 1.302 · 12:12 → 1.414
Worked Example
Inputs: 40 ft × 24 ft building, 0.75 ft eave & rake overhangs, 6:12 pitch, 20 ft² openings, 10% waste, 33.3 ft²/bundle.
- Plan with overhangs:
(40 + 1.5) × (24 + 1.5) = 41.5 × 25.5 = 1,058.25 ft² - Pitch factor (6:12):
≈ 1.118 - Sloped (no waste):
1,058.25 × 1.118 − 20 ≈ 1,163 ft² - With 10% waste:
≈ 1,279 ft²→ Squares:≈ 12.8 - Bundles (33.3 ft²/bundle):
ceil(1,279 ÷ 33.3) = 39 bundles
What Affects Waste (Order Enough)
- Roof style & complexity: hips, valleys, dormers, and cut-heavy layouts increase offcuts.
- Steeper pitches: more pieces, more staging, typically a little more waste.
- Starter & ridge/hip caps: usually come from shingles but effectively add to total usage.
- Ordering: round up to whole bundles; keep 1–2 bundles for future repairs and color matching.
3-Tab vs Architectural Shingles
Both common asphalt shingle types typically figure at ≈3 bundles per square, but coverage per bundle can vary by brand. Architectural (laminate) shingles are heavier and often last longer; 3-tab are lighter and budget-friendly. Always check the bundle coverage printed on the wrapper and override the default if needed.
Underlayment, Nails & Flashings (Quick Guide)
- Underlayment: felt #15/#30 or synthetic; coverage varies by roll. Add a margin for laps and overlaps.
- Nailing: plan ~320 nails per square (4-nail) or ~480 nails per square (6-nail/high-wind).
- Drip edge & flashing: order by linear footage of eaves/rakes and penetrations (chimneys, skylights, vents).
- Ice & water shield: cold climates often require it at eaves/valleys—check local codes.
Pro Tip
Measure overhangs carefully. A small increase (e.g., 1.0 ft vs 0.5 ft) can add dozens of square feet across a roof.
Metric vs Imperial
1 roofing square (100 ft²) equals ≈ 9.2903 m². If you switch the unit system, the calculator keeps the math consistent, but bundle coverage should match the units you’re using (e.g., set bundle coverage to ≈3.09 m² for the common 33.3 ft²/bundle equivalent).
Safety & Planning
- Use proper fall protection on steep slopes and wet surfaces.
- Stage materials so you’re not over-loading trusses in one spot.
- Ventilation matters—verify intake/exhaust to protect shingle life.
Related Project Calculators
- Paver Calculator – plan walkways, patios, and approaches around the house.
- Epoxy Calculator – estimate epoxy coverage for garage floors and interiors.
- Fence Cost Calculator – budget your boundary or privacy upgrades.