9/12 Roof Pitch: Angle, Multiplier and What It Means
Angle
36.9 degrees
9 inches of rise for every 12 inches of run, over a 1,200 square foot footprint.
At 8/12 and above the crew needs roof jacks or staging, and the labor rate goes up with it.
How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Rise9 in per 12 in run
- Footprint area, 0 to skip1200 sq ft
Slope multiplier1.25 x footprint
At 8/12 and above the crew needs roof jacks or staging, and the labor rate goes up with it.
| Pitch | 9/12 |
|---|---|
| Slope multiplier | 1.25 xmultiply footprint by this |
| Angle | 36.9 degrees |
| Grade | 75% |
| Rafter length per 12 ft of run | 15 ft |
| Roof surface for 1,200 sq ft footprint | 1,500 sq ft |
| That is | 15 squares |
Pitch compared
The whole table, so you do not have to come back for the next one.
| Pitch | Slope multiplier | Angle | Grade |
|---|---|---|---|
| 2/12 | 1.01 x footprint | 9.5 degrees | 16.7% |
| 3/12 | 1.03 x footprint | 14 degrees | 25% |
| 4/12 | 1.05 x footprint | 18.4 degrees | 33.3% |
| 5/12 | 1.08 x footprint | 22.6 degrees | 41.7% |
| 6/12 | 1.12 x footprint | 26.6 degrees | 50% |
| 7/12 | 1.16 x footprint | 30.3 degrees | 58.3% |
| 8/12 | 1.2 x footprint | 33.7 degrees | 66.7% |
| 9/12 | 1.25 x footprint | 36.9 degrees | 75% |
| 10/12 | 1.3 x footprint | 39.8 degrees | 83.3% |
| 12/12 | 1.41 x footprint | 45 degrees | 100% |
What else matters here
A 9/12 pitch is 36.9 degrees and a 75 percent grade. The multiplier is exactly 1.25, so the roof surface is a quarter larger than the flat footprint: 1,200 square feet on the plan, 1,500 square feet on the roof, a clean 15 squares.
At this angle the work changes character. Everything gets carried up rather than slid, bundles have to be broken and placed rather than stacked, and the tear off has to be controlled so nothing rides the slope into a window or a customer's car.
Steep roofs like this are common on Tudor, Victorian and story and a half houses, and often carry more valley and dormer work than a shallow roof does. Count those separately: valleys, hips and dormer returns are where a steep roof estimate actually goes wrong, not the field.
What this calculator assumes
- Pitch is written as rise over a 12 inch run. A 6/12 roof climbs 6 inches for every 12 inches across.
- The slope multiplier converts flat footprint area into real roof surface. It is the number that decides whether you order enough shingles.
- Below 2/12, shingles are not rated. Below 4/12, most manufacturers require a double underlayment. Over 8/12 you are on roof jacks and the labor price changes.
Questions people ask
What is 9/12 in degrees?
36.9 degrees, which is a 75 percent grade.
How much bigger is a 9/12 roof than its footprint?
Exactly 25 percent, since the slope multiplier at 9/12 is 1.25.
What is the slope multiplier for?
Multiply the flat footprint of the building by it to get the real surface area of the roof. A roof plan gives you the footprint, and the multiplier turns it into the area you actually have to cover.
The roof pitch calculator takes any dimensions you like and hands back the same list.