This roof pitch calculator works in both directions: measure a rise and run anywhere on the roof and get the pitch in standard x/12 form, or enter a known pitch like 6/12 and convert roof pitch to degrees, slope percent, and a rafter length multiplier.
Roof pitch drives almost every roofing decision — which materials are allowed, how underlayment must be installed, whether the roof is walkable, and how much extra surface area you pay for versus the home’s footprint. Measuring is easy: hold a level horizontally against the roof or rafter, mark 12 inches out, and measure straight down to the surface. That distance is the rise per 12 inches of run.
How to Calculate Roof Pitch From Rise and Run
Pitch is expressed as inches of vertical rise per 12 inches of horizontal run:
- Pitch (x/12): x = rise ÷ run × 12
- Angle in degrees: arctan(rise ÷ run)
- Slope percent: rise ÷ run × 100
- Rafter multiplier: √(12² + x²) ÷ 12
Example: you measure 6 inches of rise over a 12-inch run. Pitch is 6/12, the angle is arctan(0.5) = 26.57°, the slope is 50%, and the rafter multiplier is √(144 + 36) ÷ 12 = 1.118. A roof with 14 feet of horizontal run per side therefore needs rafters of 14 × 1.118 = 15.65 ft, plus overhang. The same multiplier converts footprint area to actual roof surface area for shingle estimates.
Common Roof Pitches in Degrees
Handy conversions for the pitches you will actually encounter:
- 1/12 = 4.76° — minimum for most low-slope metal systems
- 2/12 = 9.46° — minimum for asphalt shingles with special underlayment
- 3/12 = 14.04° — low-slope; shingles allowed with double underlayment
- 4/12 = 18.43° — standard minimum for normal shingle installation
- 5/12 = 22.62° and 6/12 = 26.57° — the most common residential pitches
- 8/12 = 33.69° — steep; roof jacks recommended
- 10/12 = 39.81° and 12/12 = 45° — very steep, common on A-frames and Victorians
Anything under 2/12 is considered a flat or low-slope roof and needs membrane roofing (EPDM, TPO), not shingles.
Walkability, Safety, and Material Limits by Pitch
Pitch determines how a roof can be worked on and what it costs:
- 0/12–3/12: easily walkable, but drainage is slow — check material minimums.
- 4/12–6/12: comfortably walkable for most people; standard staging is fine.
- 7/12–9/12: steep — roof jacks, toe boards, and fall protection are strongly recommended.
- 10/12 and up: not walkable; requires scaffolding or professional steep-roof equipment.
Steeper roofs also cost more per square of shingles installed — labor premiums of 20–50% are typical above 8/12 — but they shed water and snow faster and tend to have longer shingle life. Because surface area grows with the rafter multiplier, a 12/12 roof has 41% more area than a flat roof over the same footprint.
Frequently Asked Questions
How do you calculate roof pitch?
Hold a level horizontally against the roof surface or a rafter, mark a point 12 inches from where it touches, and measure vertically from that mark down to the roof. That measurement is the rise per 12 inches of run — a 6-inch measurement means a 6/12 pitch.
What is a 4/12 roof pitch in degrees?
A 4/12 roof pitch is 18.43 degrees, or a 33.3% slope. It rises 4 inches for every 12 inches of horizontal run and is the minimum pitch for standard asphalt shingle installation without special underlayment requirements.
How do I convert roof pitch to degrees?
Divide the rise by 12 and take the arctangent: degrees = arctan(x ÷ 12). For a 6/12 pitch, arctan(6 ÷ 12) = arctan(0.5) = 26.57°. Going the other way, multiply the tangent of the angle by 12 to get the x in x/12.
What is the most common roof pitch?
Most US homes have a roof pitch between 4/12 and 9/12, with 6/12 (26.57°) being the most common for gable roofs. Ranch homes often use 4/12–5/12, while colonial and Victorian styles run 8/12–12/12. Low-slope roofs under 2/12 are mostly limited to commercial buildings and porches.
What roof pitch is walkable?
Roofs up to about 6/12 (26.57°) are generally walkable with soft-soled shoes and dry conditions. From 7/12 to 9/12 you need roof jacks and fall protection, and pitches of 10/12 or steeper require scaffolding or steep-assist equipment and are best left to professionals.