Estimate squares, shingle bundles, underlayment, and cost for your roof.
Pitch Multiplier Table
| Pitch | Angle | Multiplier | Walk On? |
|---|
| 0/12 | 0° | 1.000 | Yes |
| 4/12 | 18.4° | 1.054 | Yes (careful) |
| 6/12 | 26.6° | 1.118 | With caution |
| 8/12 | 33.7° | 1.202 | Difficult |
| 10/12 | 39.8° | 1.302 | Harness required |
| 12/12 | 45° | 1.414 | Harness required |
Shingle Types and Lifespan
| Type | Cost/Square | Lifespan | Bundles/Square |
|---|
| 3-Tab Asphalt | $80–100 | 15–20 years | 3 |
| Architectural (dimensional) | $100–150 | 25–30 years | 3–4 |
| Premium/Designer | $150–300 | 30–50 years | 4–5 |
| Metal roofing | $300–700 | 40–70 years | N/A (panels) |
When to Replace vs. Repair
Replace if: shingles are curling, cracking, or missing granules in patches; the roof is past 80% of its expected lifespan; there are more than 2 layers of shingles already; or you see daylight through the decking from the attic. Repair when damage is isolated to a few shingles after a storm or near a single vent flashing. A professional inspection runs $150-$300 and can save thousands by catching problems early.
How to Use This Roofing Calculator
Enter roof dimensions or footprint area and pitch. The calculator estimates shingles (bundles/squares), underlayment, ridge caps, and nails needed.
Formula & How It Works
Roof Area = Footprint × Slope Factor (e.g., 4/12 pitch = 1.054, 8/12 = 1.202). Squares = Area / 100. Bundles = Squares × 3. Add 10-15% for waste and starter strips.
Calculation Example
House footprint 1,500 sq ft, 6/12 pitch: Roof area = 1,500 × 1.118 = 1,677 sq ft = 16.77 squares. Order 51 bundles (+ waste) = ~55 bundles of 3-tab shingles.
Expert Tips
Steeper roofs need more material but last longer (water sheds faster). Architectural shingles cost 20% more than 3-tab but last 50% longer and resist wind better. Always install an ice and water shield at eaves.