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.
United States — national average · 2026 prices
Material only unless stated as installed. Excludes tax, permits and local labour. Verify with local suppliers — see how we calculate.
How this calculator works
Every figure above comes from the formula below, applied to the assumptions listed. Nothing is looked up from a hidden table — you can reproduce the result by hand.
Formula
pitch = rise ÷ run × 12, expressed as X:12
angle = arctan(rise ÷ run), in degrees
slope factor = √(rise² + run²) ÷ run
rafter length = slope factor × run
Assumptions & limits
- Rise and run must be in the same unit. Pitch, angle and slope factor are ratios, so they are unit-independent; the unit selector only sets the unit the rafter length is reported in.
- Rafter length is the straight run along the slope. It excludes overhang, ridge-board thickness and the birdsmouth cut.
- Pitch categories follow common US roofing practice: below 4:12 is low slope, 4:12 to 9:12 conventional, above 9:12 steep. Low-slope roofs have their own underlayment requirements.
Worked example
A rise of 6 inches over a run of 12 inches
- Pitch = 6 ÷ 12 × 12 = 6:12
- Angle = arctan(6 ÷ 12) = 26.6°
- Slope factor = √(6² + 12²) ÷ 12 = 13.416 ÷ 12 = 1.1180
- Rafter length = 1.1180 × 12 = 13.42 (in the unit you entered)
Result:A 6:12 pitch at 26.6°, slope factor 1.118 — so sloped roof area is 11.8% larger than the footprint.
Built and maintained by Christoph Ballmer, Honeygoat GmbH
Method and constants last checked against the calculator code on August 17, 2026. Independent trade review is not yet in place for this calculator — see how we handle review.
Read the site-wide calculation methodology · estimate vs. quote and safety limits
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.
Pitch, angle and slope factor — quick table
| Pitch | Angle | Slope factor | Walkability |
|---|---|---|---|
| 3:12 | 14.0° | 1.031 | Easy |
| 4:12 | 18.4° | 1.054 | Comfortable |
| 6:12 | 26.6° | 1.118 | Careful footing |
| 8:12 | 33.7° | 1.202 | Roof jacks advised |
| 10:12 | 39.8° | 1.302 | Staging required |
| 12:12 | 45.0° | 1.414 | Specialist territory |
Pitch decides the material
Standard asphalt shingles want 4:12 or steeper; between 2:12 and 4:12 they are allowed only over doubled or ice-and-water underlayment per the code, and below 2:12 shingles are out — that is membrane territory (EPDM, TPO). Metal panels reach lower slopes depending on the profile. Measure the pitch first, because it filters the material list before any cost math.
Common mistakes
- Quoting degrees to a roofer. The US trade speaks in rise per 12 — say “six twelve”, not “26.6 degrees”. The calculator shows both for exactly this translation.
- Slope factor on the wrong area. The factor scales the horizontal FOOTPRINT including overhangs — measured at the eaves, not the interior floor plan.
- Measuring on a wavy surface. Read rise-over-run on the underside of a rafter in the attic, or on a level held against the shingles — not across curled shingle edges.
- Assuming one pitch. Porches, dormers and additions often carry their own pitch; measure each plane before ordering.
With the pitch in hand, the roofing calculator turns footprint × slope factor into squares and bundles, and the replacement cost calculator prices 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.