MaterialScopeHow this calculation works
Enter measurements above to see the worked calculation.
Use actual coverage, not just a bundle count
A roofing square is 100 square feet. Bundle coverage depends on the selected shingle. The example coverage is approximately one-third of a square; use the manufacturer’s listed coverage for your product. Starter strips, ridge caps, underlayment and fasteners are separate products; the roofing calculator estimates starter, ridge cap, underlayment and drip edge from your roof edges.
Keep the geometry simple
The footprint method assumes one consistent pitch over the measured horizontal footprint, including overhangs. Complex roofs with dormers, valleys or mixed pitches need separate measured sections. This tool does not determine roof structure, flashing requirements or safe access.
Product reference: Owens Corning roofing product documents. Confirm the current label for your chosen product.
The slope adjustment
The surface-area multiplier is the square root of one plus (rise ÷ 12) squared. A 6:12 pitch gives a multiplier of about 1.118. A 40 by 30-foot footprint therefore has about 1,341.64 square feet of roof surface before extra material. The same multiplier works for gable and hip roofs, as long as every plane has the same pitch.
The full materials list
Beyond field shingles, the calculator estimates four items from your roof edges. Starter strip runs along the eaves and rakes. Drip edge covers the same edges in straight pieces. Ridge cap covers ridges and hips. Underlayment covers the whole roof surface. Each uses the same extra-material allowance and rounds up to whole bundles, pieces or rolls. Enter 0 for any edge you will not cover.
| Example: 40 × 30 ft gable, 6:12 | Measurement | With 10% extra |
|---|---|---|
| Field shingles | 1,341.64 ft² of roof | 45 bundles |
| Starter strip (100 ft/bundle) | 80 ft eaves + 67 ft rakes | 2 bundles |
| Drip edge (10-ft pieces) | 147 ft of edges | 17 pieces |
| Ridge cap (25 ft/bundle) | 40 ft of ridge | 2 bundles |
| Underlayment (1,000 ft²/roll) | 1,341.64 ft² of roof | 2 rolls |
Starter, ridge cap and underlayment coverage vary widely by product, so the defaults are editable starting points. Read the coverage on the product you will buy. Some installers do not use starter on rakes; set the rake length to 0 in that case and add it to the drip edge separately. Flashing, vents, ice barrier and fasteners are not included. Not sure how to find your edge lengths? See how to measure a roof.
Make the estimate your own
Measure the actual area, choose your product and update the allowance. Costs use the price you enter. Delivery, tax, labor and preparation are excluded unless this tool has a separate field for them. The result rounds whole packages up; displayed decimal quantities are not supplier order increments.
Before you order
- Check dimensions and units, including depth and openings.
- Confirm the selected product’s coverage, yield or density.
- Ask your supplier about package sizes, minimum orders and delivery access.
- Keep a copy of your measurements with your material plan.
Method v1.0 · Updated October 21, 2026. Read our methodology.