Roof Pitch Calculator
Enter the roof's rise and run — most often the rise over a standard 12-inch run. The calculator returns the pitch as x-in-12, the angle in degrees, the grade as a percentage and the slope (rafter) multiplier you use to convert a horizontal run into rafter length. Add the horizontal run to get the rafter line length directly.
Your measurements
Vertical rise over the run below (a 6-in-12 roof rises 6 in).
Horizontal run the rise is measured over — usually 12 in.
Pitch
- Rise : run
- 6 : 12
- Pitch (per 12)
- 6-in-12
Roof pitch
6-in-12
26.6° · 50% grade
Roof geometry
- Angle
- 26.6°
- Grade
- 50%
- Slope factor
- 1.118×
Estimates only. Verify against your supplier's coverage figures before ordering.
The formula
Pitch = rise ÷ run × 12 · Angle = arctan(rise ÷ run) · Slope factor = √(rise² + run²) ÷ run
Example: A 6-in rise over a 12-in run is a 6-in-12 pitch — a 26.57° roof, a 50% grade, and a 1.118 slope factor. Over a 14-ft horizontal run the rafter line is 15.65 ft.
How it works
- 1Roof pitch is the rise (vertical) over the run (horizontal), expressed as a number over 12 — e.g. 6-in-12.
- 2Convert any rise/run to x-in-12 by computing rise ÷ run × 12.
- 3The angle in degrees is arctan(rise ÷ run); the grade percentage is rise ÷ run × 100.
- 4The slope factor √(rise² + run²) ÷ run turns a horizontal run into rafter length and footprint area into actual roof area.
- 5Multiply the horizontal run (wall to ridge) by the slope factor for the rafter line length — then add overhang and subtract half the ridge thickness.
Frequently asked questions
How do you calculate the pitch of a roof?
Measure how many inches the roof rises over a level 12-inch run. Hold a level horizontally against the roof, measure 12 inches out, then measure straight down to the roof — that drop is the rise. A 6-inch drop over 12 inches is a 6-in-12 pitch.
What's the difference between pitch, slope and angle?
They describe the same steepness three ways. Pitch (or slope) is the rise-over-12 ratio builders use (6-in-12). The angle is that ratio in degrees (6-in-12 ≈ 26.6°). Grade is the rise ÷ run as a percentage (6-in-12 = 50%).
What is the slope factor used for?
The slope factor is how much longer the sloped roof is than its flat footprint. Multiply the horizontal run by it for rafter length, or multiply the building's footprint area by it to get the actual roof surface area for ordering shingles.
What is a standard roof pitch?
Most residential roofs fall between 4-in-12 and 9-in-12. Below 3-in-12 is considered low-slope (and needs different materials); 12-in-12 (45°) and steeper are steep-slope roofs.