Understanding Roofing Measurements
Roofing materials are sold by the "square" - a unit equal to 100 square feet of roof coverage. Most asphalt shingles require 3 bundles per square, though premium shingles may require 4 bundles. This calculator helps you determine exactly how many bundles you need based on your roof size and type.
Roof Pitch Multipliers
The pitch of your roof affects the total surface area. A steeper roof has more surface area than a flat roof over the same footprint.
| Pitch | Angle | Multiplier | Walkability |
|---|---|---|---|
| 4/12 | 18.4 deg | 1.054 | Easy |
| 6/12 | 26.6 deg | 1.118 | Moderate |
| 8/12 | 33.7 deg | 1.202 | Difficult |
| 10/12 | 39.8 deg | 1.302 | Very Difficult |
| 12/12 | 45.0 deg | 1.414 | Steep |
Shingle Types Comparison
| Type | Lifespan | Cost/Bundle | Wind Rating |
|---|---|---|---|
| 3-Tab | 15-20 years | $25-35 | 60-70 mph |
| Architectural | 25-30 years | $35-50 | 110-130 mph |
| Premium | 30-50 years | $50-100 | 130+ mph |
| Metal | 40-70 years | $100-300 | 140+ mph |
Additional Materials Needed
- Underlayment: Felt or synthetic, 1 roll covers 4 squares
- Drip Edge: 10-foot sections, perimeter + 10%
- Ridge Cap: 20 linear feet per bundle
- Starter Strip: 1 bundle per 100 linear feet of eaves
- Roofing Nails: 2-2.5 lbs per square
- Ice & Water Shield: First 3-6 feet from eaves in cold climates
Roofing Tips
- Always order 10-15% extra for waste and future repairs
- Check local codes for underlayment and ice shield requirements
- Install in temperatures above 40F for proper seal activation
- Ensure proper attic ventilation to maximize shingle life
- Consider hiring professionals for steep or complex roofs
- Get multiple quotes and check contractor licensing/insurance
When to Replace Your Roof
Signs you need a new roof: curling or missing shingles, granule loss in gutters, daylight visible in attic, age over 20 years for asphalt, leaks or water stains on ceilings, and sagging roof deck. Address issues promptly to prevent interior damage.