Pitch12

Jobsite geometry

Roof Pitch Calculator

Enter any one value — rise, run, angle, or X-in-12 — and the others update instantly. The math runs on this device. Nothing is uploaded.

Pitch

6:12

Angle

26.57°

run rise rafter °

Grade

50%

Slope factor

1.1180

Rafter

13.416 in

In inches, fractions such as 6 1/2 or 5-3/8 are accepted.

Pitch slider 6:12

Roof area from pitch

Optional. Uses the slope factor on a simple rectangle plan.

Rise 6 in · Run 12 in

What roof pitch means

Roof pitch is the slope of a roof expressed as rise over a 12-inch run. A 6:12 pitch rises 6 inches for every 12 inches of horizontal run. The same slope can also be written as an angle in degrees or as a percent grade. This calculator keeps all three in sync, and it also gives the rafter length and the slope factor used to turn a floor-plan footprint into roof surface.

In the United States, carpenters almost always speak in X-in-12. Architects often prefer degrees. Material takeoffs care about the slope factor: multiply the building’s plan area by that factor to estimate the roof covering on a simple gable or shed, before overhangs and wasted cuts.

How to measure rise and run

The attic method is the most common. Place one end of a level against the underside of a rafter, then adjust the level until the bubble is centered so the tool is truly horizontal. From the point where the level meets the rafter, measure 12 inches along the level. At that 12-inch mark, measure straight up to the rafter. That vertical distance is the rise. If you measure 6 inches, the pitch is 6:12.

From outside, rise is the height from the top of the wall plate to the ridge. Run for one side of a gable is half the building width (plus any overhang you want in the rafter length). On a phone, use Measure with phone and lay the device screen-up on a rafter. The page reads the tilt relative to gravity; it does not send motion data anywhere.

The math

Treat the roof as a right triangle. Run is the adjacent side, rise is the opposite side, and the rafter is the hypotenuse:

Worked example: rise 6 in, run 12 in. Angle = arctan(0.5) = 26.57°. Grade = 50%. Rafter = √(36 + 144) = 13.416 in. Slope factor = 13.416 ÷ 12 = 1.118. A 20 × 16 ft plan (320 sq ft) on a matching gable then has about 358 sq ft of roof surface, or 3.58 squares, before waste.

Common pitches

These figures are geometry, not a building-code table. Always check the shingle manufacturer and the local building department for the roof you are actually building.

Pitch Angle Grade Factor Notes
3:1214.04°25.00%1.031Low slope; many shingles need extra underlayment.
4:1218.43°33.33%1.054A common minimum for standard asphalt shingles.
6:1226.57°50.00%1.118Very common residential pitch; still walkable with care.
8:1233.69°66.67%1.202Steeper; plan extra safety gear.
12:1245.00°100.00%1.414Equal rise and run. Roof area is about 41% larger than the plan.

FAQ

What is a 4/12 roof pitch in degrees?

4:12 is arctan(4/12) = 18.43°, a 33.33% grade, slope factor 1.054.

What is a 6/12 roof pitch in degrees?

6:12 is 26.57°, a 50% grade, slope factor 1.118. For every 12 inches of run the rafter is 13.416 inches long.

What is a 12/12 roof pitch in degrees?

12:12 is exactly 45°. Rise equals run. The slope factor is √2 ≈ 1.414.

What is a roof pitch multiplier?

It is the same number as the slope factor: √(1 + (rise/run)²). Multiply a simple rectangular plan area by this factor to estimate roof surface. It does not add hips, valleys, waste, or starter courses.

Does this follow building code?

No. Pitch12 only converts geometry. Span tables, snow load, fastener schedules, and shingle limits come from the manufacturer and your local building department. This is not engineering advice.