3/12 Roof Pitch: Angle, Multiplier and What It Means
Angle
14 degrees
3 inches of rise for every 12 inches of run, over a 1,200 square foot footprint.
Between 2/12 and 4/12 most shingle manufacturers require a doubled underlayment or the warranty is void.
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.
- Rise3 in per 12 in run
- Footprint area, 0 to skip1200 sq ft
Slope multiplier1.03 x footprint
Between 2/12 and 4/12 most shingle manufacturers require a doubled underlayment or the warranty is void.
| Pitch | 3/12 |
|---|---|
| Slope multiplier | 1.03 xmultiply footprint by this |
| Angle | 14 degrees |
| Grade | 25% |
| Rafter length per 12 ft of run | 12.37 ft |
| Roof surface for 1,200 sq ft footprint | 1,237 sq ft |
| That is | 12.4 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 3/12 pitch is 14 degrees and a 25 percent grade. It is still inside the low slope band where asphalt shingles need a doubled underlayment application, and most shingle manufacturers say the same thing in their own installation instructions, which is the document a warranty claim gets read against.
The multiplier is 1.03, so a 1,200 square foot footprint is 1,237 square feet of roof. On a takeoff that difference is about a third of a square, which is inside the waste allowance rather than something to price separately.
This is a comfortable pitch to walk and a common one on porches, additions and ranch houses. It sheds water well enough in rain but holds snow, so in a snow region check the load path before adding anything heavy on top of it.
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 3/12 in degrees?
14 degrees, which is a 25 percent grade.
Do shingles need special underlayment at 3/12?
Yes. Anything from 2/12 up to but not including 4/12 is a low slope application under the IRC and needs a doubled underlayment layer.
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.