Roof Pitch Calculator
Find your roof pitch from a simple rise-and-run measurement — get the pitch in X-in-12, the angle in degrees, the slope factor and the rafter length per foot of run.
How to calculate roof pitch
Roof pitch describes how steep a roof is, written as the vertical rise for every 12 inches of horizontal run. A roof that climbs 6 inches over a 12-inch run is a 6:12 pitch. To measure it, hold a level out horizontally from the roof, mark 12 inches along it, and measure straight down to the roof surface — that drop in inches is your rise.
pitch = (rise ÷ run) × 12 · angle = arctan(rise ÷ run) · slope factor = √(rise² + run²) ÷ run
The slope factor is the number you actually use to buy materials: multiply your flat building footprint by it to get the true sloped roof area. For example, a 6:12 roof has a slope factor of about 1.118, so a 2,000 sq ft footprint becomes roughly 2,236 sq ft of roof.
Common roof pitches, angles and slope factors
| Pitch | Angle | Slope factor | Category |
|---|---|---|---|
| 3:12 | 14.0° | 1.031 | Low slope |
| 4:12 | 18.4° | 1.054 | Conventional |
| 6:12 | 26.6° | 1.118 | Conventional |
| 8:12 | 33.7° | 1.202 | Conventional |
| 10:12 | 39.8° | 1.302 | Steep |
| 12:12 | 45.0° | 1.414 | Steep |
Once you know your pitch and slope factor, head to the roofing material calculator to turn your roof size into squares, bundles and a shopping list, or the roof replacement cost calculator to price the job.
Frequently asked questions
How do I calculate my roof pitch?
Roof pitch is the rise (vertical) over the run (horizontal), expressed per 12 inches of run. Measure the rise over a 12-inch level run and read it directly — a 6-inch rise over 12 inches of run is a 6:12 pitch. This calculator takes any rise and run, scales it to a 12-inch base, and also gives the angle in degrees and the slope factor.
What is the most common roof pitch?
Most residential roofs fall between 4:12 and 9:12. Anything from about 4:12 to 9:12 is considered a conventional walkable slope; below 4:12 is a low slope that often needs different roofing, and 10:12 and steeper is a steep slope that needs extra safety equipment and labor.
What is the slope factor and why does it matter?
The slope factor is the multiplier that converts your flat footprint area into the actual sloped roof area. A 6:12 roof has a slope factor of about 1.118, so 2,000 sq ft of footprint is about 2,236 sq ft of roof. You need the true sloped area — not the footprint — to order the right amount of roofing material.
How do I convert roof pitch to degrees?
The angle in degrees is the inverse tangent of rise ÷ run. A 6:12 pitch is arctan(6 ÷ 12) ≈ 26.57°, and a 12:12 pitch is exactly 45°. This calculator shows the degree angle next to the X:12 pitch automatically.
What roof pitch is walkable?
Roofs up to about 6:12 are generally comfortable to walk with normal caution. From 7:12 to 9:12 most people want roof jacks or a harness, and 10:12 and steeper is considered steep — it needs fall protection and usually costs more to roof because of the slower, harder work.