📐 Roof Pitch Calculator

What a roof pitch of X/12 means

A roof pitch of X/12 means the roof rises X inches for every 12 inches it runs horizontally. A 6/12 roof is 26.57°, a 50% grade, has a rafter multiplier of 1.1180 and a hip/valley multiplier of 1.5000.

• Degrees = arctan(X ÷ 12). Going the other way, rise per 12 = 12 × tan(degrees), so a 30° roof is 6.93/12.
• Percent grade = X ÷ 12 × 100. A 4/12 roof is a 33.3% grade.
• Rafter (common) multiplier = √(1 + (X ÷ 12)²). Multiply the run by it for rafter length, or the footprint by it for sloped roof area.
• Hip/valley multiplier = √(2 + (X ÷ 12)²). Multiply the common run by it for the length of a 45° hip or valley, the figure you need for hip-and-ridge cap and valley metal.

What is a roof pitch calculator?

A roof pitch calculator converts the vertical rise and horizontal run of a roof into the four numbers contractors actually use: the pitch ratio (e.g. 6/12), the slope percentage, the roof angle in degrees, and the pitch multiplier used to convert flat (plan) area into actual sloped roof area. Enter your rise and run above to get all four values instantly — free, no signup, works on mobile.

Roof pitch table: 1/12 to 24/12

Every whole pitch from 1/12 to 24/12, worked out by the same functions the calculator above runs. Read across for the angle, the grade and both multipliers.

Printable version with a CSV download and a slope diagram: the roof pitch chart.

How to measure your roof pitch

You need a level at least 24 in long, a tape measure and a pencil. Mark the level 12 in from one end before you start.

Level-and-tape method (at the rake edge or on the roof):

1. Work from a ladder at the gable end if you can, rather than walking the roof.
2. Touch the end of the level you measured from to the roof surface and hold the level out horizontally over the down-slope side, bubble centred.
3. At the 12 in mark, measure straight down (plumb) from the bottom of the level to the roof surface.
4. That distance in inches is the rise. A 6 in measurement means a 6/12 pitch. Enter it above with a run of 12.

From the attic (no ladder on the roof):

1. Touch the end of the level you measured from to the bottom edge of a rafter, with the level reaching toward the ridge.
2. Bring the level to horizontal.
3. At the 12 in mark, measure plumb up from the level to the bottom edge of the rafter.
4. That measurement is the rise per 12 in. Check two or three rafters; a sagging rafter reads low.

No access at all? Measure the building width and the ridge height above the wall plate. Pitch = ridge height ÷ (width ÷ 2) × 12, so a 7.5 ft rise over a 30 ft gable is 7.5 ÷ 15 × 12 = 6/12.

Minimum roof pitch by roofing material

The International Residential Code (2021 IRC, Section R905) sets the lowest slope each roof covering may be installed on. Asphalt shingles need at least 2:12, and between 2:12 and 4:12 they need two layers of underlayment. Your local code and the manufacturer's instructions can be stricter.

Check one pitch against every material with the minimum roof pitch calculator.

Sources (checked 2 October 2026): Minimum roof slopes by roofing material, 2021 IRC Section R905 (Building Code Trainer); Asphalt shingles, IRC R905.2 (City of Hopkins, MN building division).

9/12 Roof Pitch (12/9 Pitch)

A 9/12 pitch — sometimes written as a 12/9 pitch — rises 9 inches for every 12 inches of horizontal run. That works out to an angle of about 36.87°, a slope of 75%, and a pitch multiplier of 1.2500. To estimate the actual roof surface area on a 9/12 roof, multiply the building footprint by 1.25. A 9/12 is considered steep — most crews use roof jacks, harnesses, and staging.

10/12 Roof Pitch

A 10/12 pitch rises 10 inches per 12 inches of run. The roof angle is approximately 39.81°, slope is 83.3%, and the pitch multiplier is 1.3017. Multiply your flat footprint by 1.3017 to get the true sloped area. 10/12 is on the upper edge of typical residential pitches — expect higher labor costs and mandatory fall protection.