Roofing Calculator
Calculate how many bundles of shingles, roofing squares, underlayment rolls, and ridge caps you need for your roofing project. Enter your roof dimensions and pitch to get instant material estimates.
How to Calculate Roofing Materials
Estimating roofing materials involves converting your ground-level measurements to actual roof area using the pitch multiplier:
- Measure the footprint: Measure your building's length and width from the ground to get the flat area.
- Apply the pitch factor: Multiply flat area by the pitch multiplier to get actual roof surface area.
- Add waste: Add 10-15% for cuts, waste, hips, and valleys.
- Convert to squares: Divide total area by 100 to get roofing squares.
- Calculate bundles: Multiply squares by 3 to get bundles of standard asphalt shingles.
Understanding Roof Pitch
Roof pitch is expressed as rise over run (e.g., 6/12 means the roof rises 6 inches for every 12 inches of horizontal run). Steeper pitches require more material because the actual roof surface area is larger than the building footprint.
- 4/12 pitch: Low slope, adds about 5.4% to flat area
- 6/12 pitch: Standard residential, adds about 11.8% to flat area
- 8/12 pitch: Moderately steep, adds about 20.2% to flat area
- 12/12 pitch: Very steep (45 degrees), adds about 41.4% to flat area
Shingles Per Square
One roofing "square" equals 100 square feet of roof area. Standard 3-tab and architectural asphalt shingles require 3 bundles per square. Some premium or heavyweight shingles may require 4-5 bundles per square. Always verify with the manufacturer's coverage specifications.
Underlayment Types
- Felt (tar paper): 15 lb or 30 lb felt. Most affordable option. Standard rolls cover approximately 400 sq ft.
- Synthetic underlayment: More durable and tear-resistant. Typically covers 1,000 sq ft per roll. Preferred for most modern installations.
- Ice and water shield: Self-adhering membrane used in valleys, eaves, and around penetrations. Required by code in cold climates.
Signs You Need a Roof Replacement
- Shingles are curling, cracking, or missing
- Granules collecting in gutters
- Roof is over 20 years old
- Daylight visible through roof boards in attic
- Sagging areas on the roof deck