Roof Pitch Calculator: Multiplier, Angle and Rafter Length
Pitch is written as rise over a 12 inch run. This turns that into the three numbers you actually use: the multiplier for ordering material, the angle for cutting, and the rafter length per foot of run.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- Rise6 in per 12 in run
- Footprint area, 0 to skip1200 sq ft
Slope multiplier1.12 x footprint
| Pitch | 6/12 |
|---|---|
| Slope multiplier | 1.12 xmultiply footprint by this |
| Angle | 26.6 degrees |
| Grade | 50% |
| Rafter length per 12 ft of run | 13.42 ft |
| Roof surface for 1,200 sq ft footprint | 1,342 sq ft |
| That is | 13.4 squares |
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.
The three ways to say the same thing
A 6/12 roof rises 6 inches over a 12 inch run. That is a 26.57 degree angle, a 50 percent grade, and a slope multiplier of 1.118. Roofers use pitch, framers use degrees when they are cutting, and engineers use grade.
The multiplier is the one that touches your wallet. Footprint times the multiplier is the real surface, and the real surface is what you order shingles against.
The pitch bands that change the job
Under 2/12, asphalt shingles are not rated at all and the roof needs a membrane. Between 2/12 and 4/12, most manufacturers require doubled underlayment or the warranty is void, and that requirement is in the installation instructions, not in the sales brochure.
From 4/12 to 7/12 is normal walkable work. At 8/12 and above the crew needs roof jacks or staging, production drops, and the labor rate goes up with it. Above 12/12 many roofers will not quote at all without a scaffold line.
This is why pitch belongs on the estimate. A 10/12 roof is not the same job as a 5/12 roof of the same size and the price should say so.
Measuring pitch without getting on the roof
Hold a level horizontally against the rake board or a gable end, mark 12 inches along it, and measure straight down from that mark to the roof surface. That drop is the rise.
From inside, do the same against a rafter in the attic. It is safer, and on a house with a low overhang it is often the only way to get a clean 12 inches.
Questions people ask
What is the slope multiplier for a 6/12 roof?
1.118. Multiply the building footprint by 1.118 to get the actual roof surface area for a 6/12 pitch.
What is 6/12 pitch in degrees?
26.6 degrees. The angle is the arctangent of the rise divided by 12.
Roofing estimate template and Roofing invoice template, free, no signup, PDF Word and Excel.
Common sizes, worked out
Each row is this calculator run with those numbers when the page was built. Type the same numbers in above to see every line of the working.
| Example | What it assumes | Angle |
|---|---|---|
| 2/12 pitch | 2 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 9.5 degreesBetween 2/12 and 4/12 most shingle manufacturers require a doubled underlayment or the warranty is void. |
| 3/12 pitch | 3 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 14 degreesBetween 2/12 and 4/12 most shingle manufacturers require a doubled underlayment or the warranty is void. |
| 4/12 pitch | 4 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 18.4 degrees |
| 5/12 pitch | 5 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 22.6 degrees |
| 6/12 pitch | 6 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 26.6 degrees |
| 7/12 pitch | 7 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 30.3 degrees |
| 8/12 pitch | 8 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 33.7 degreesAt 8/12 and above the crew needs roof jacks or staging, and the labor rate goes up with it. |
| 9/12 pitch | 9 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 36.9 degreesAt 8/12 and above the crew needs roof jacks or staging, and the labor rate goes up with it. |
| 10/12 pitch | 10 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 39.8 degreesAt 8/12 and above the crew needs roof jacks or staging, and the labor rate goes up with it. |
| 12/12 pitch | 12 inches of rise for every 12 inches of run, over a 1,200 square foot footprint. | 45 degreesAt 8/12 and above the crew needs roof jacks or staging, and the labor rate goes up with it. |