How the math works
A roof’s surface is larger than the footprint beneath it. The steeper the pitch, the bigger the difference. The pitch multiplier is √(1 + (rise ÷ 12)²): a 6/12 roof is about 11.8% larger than its footprint; a 12/12 roof is about 41.4% larger.
Checking your estimate
- Find the roof section of the carrier’s estimate and note total squares and the waste percentage.
- Compare those figures with the result here. Differences over 5–10% deserve a closer look.
- Check for steep charges (often 7/12 and up) and high-roof charges for two-story sections.
- Confirm ridge cap, starter, drip edge and valley materials are listed separately.
Limits of a footprint calculation
Complex roofs with multiple pitches, dormers and valleys need measuring by plane. Aerial measurement reports or a field measurement will always beat a footprint estimate — use this as a sanity check.
Questions about this tool
What’s a ‘square’?
100 square feet of roof surface. A typical Georgia two-story home might have 25 to 40 squares.
Why does waste change by roof type?
Hips, valleys and dormers require more cutting, so more material ends up as scrap.