Footprint, then pitch, then squares
Enter the horizontal roof rectangle or a measured footprint, then the rise per 12. A 6:12 pitch is a rise, not an angle — do not type degrees in the rise field. The pitch factor stretches footprint into roof surface.
A square is 100 ft² of coverage. Architectural shingles are often 3 bundles per square; some products differ. Use the selected package, not a universal three.
Waste, ridge and underlayment are not a vibe
Simple gables might live at 10–15% waste. Valleys, hips, dormers and steep cut-up roofs need more, entered as waste, not buried in length. Ridge cap, starter, drip edge and underlayment are separate takeoffs.
Underlayment roll coverage is a 1,000 ft² planning assumption before required overlap unless you replace it with the roll you will buy.
Do it in order
- Measure the horizontal footprint and the rise per 12.
- Convert sloped area to squares, then to bundles using the selected product.
- Add ridge, starter, underlayment and flashing as their own lines, with waste visible.
Worked example — 40 ft × 30 ft footprint, 6:12, 3 bundles/square
A 6:12 factor is about 1.118. Footprint 1,200 ft² becomes ~1,342 ft² of roof, 13.42 squares before waste. At 10% waste that is 14.77 squares, rounding to whole squares and then to bundles from the product you selected.
Planning boundary
This is a coverage method. It does not design structure, ventilation, drainage or a weather-tight specification.
Can I skip pitch on a low slope?
Even 3:12 is not 1.000. Enter the rise. A flat roof is a different system.
Are three bundles always a square?
Only if that product says so. Read the wrapper.
Does this design ventilation?
No. It estimates covering. Structure, intake/exhaust and ice barrier stay with the spec.