Roof pitch factors
Turn a horizontal footprint into sloped roof area. Find your multiplier first.
Free to use. No registration. No uploads.
Your pitch factor
Assumes a straight, uniform roof plane. Run is horizontal distance, never the sloped rafter length.
Estimates only. Verify measurements and product requirements before use.
From pitch to area
Sloped area = horizontal area × factor
For 6/12: √(1 + 0.5²) = √1.25 = 1.118033989. A 1,200 sq ft footprint becomes 1,341.64 sq ft before waste.
| Pitch | Factor | Angle |
|---|---|---|
| 0/12 | 1.000000 | 0.00° |
| 1/12 | 1.003466 | 4.76° |
| 2/12 | 1.013794 | 9.46° |
| 3/12 | 1.030776 | 14.04° |
| 4/12 | 1.054093 | 18.43° |
| 5/12 | 1.083333 | 22.62° |
| 6/12 | 1.118034 | 26.57° |
| 7/12 | 1.157704 | 30.26° |
| 8/12 | 1.201850 | 33.69° |
| 9/12 | 1.250000 | 36.87° |
| 10/12 | 1.301708 | 39.81° |
| 11/12 | 1.356568 | 42.51° |
| 12/12 | 1.414214 | 45.00° |
| 13/12 | 1.474317 | 47.29° |
| 14/12 | 1.536591 | 49.40° |
| 15/12 | 1.600781 | 51.34° |
| 16/12 | 1.666667 | 53.13° |
| 17/12 | 1.734054 | 54.78° |
| 18/12 | 1.802776 | 56.31° |
Common questions
What does a pitch factor multiply?
Multiply the horizontal projected area by the factor to estimate actual roof surface area. It is not a waste allowance.
Is a 12/12 roof twice its footprint?
No. The factor is √2, approximately 1.414214. A 1,000 sq ft footprint has about 1,414.2 sq ft of roof surface.
Does a flat roof have a factor?
At 0/12 the geometric factor is 1. Real low-slope roofs still need drainage design and material-specific detailing.
Does the table include waste?
No. The table describes geometry only. Add waste after calculating all roof sections.
Can I use one factor for a complex roof?
Only when every roof plane uses that pitch. Otherwise split it into non-overlapping projected sections with separate factors.