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Construction glossary · Units of measure

What is roof pitchin construction?

Roof pitch is the slope of a roof, expressed as inches of vertical rise per 12 inches of horizontal run, such as 6:12. Estimators care about pitch because it converts flat plan area into actual sloped roof area through a slope factor, and roofing material and labor follow the sloped surface, not the footprint. At a 6:12 pitch the slope factor is 1.118, so 1,000 sf of plan area is about 1,118 sf of roof surface.

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Updated June 2026 · Reviewed by the Ruh construction team

Stated as rise : 12 run4:12 = ~18.4 degreesSlope factor adds roof area

How roof pitch is expressed

4 in12 in4:121.054 slope factor
The definition

Roof pitch, explained.

Roof pitch is the steepness of a roof, stated as inches of rise per 12 inches of horizontal run. On commercial drawings you will see it called out on roof plans, building sections, and wall sections, usually as a small triangle with the rise number over a 12, and the roofing spec lists a minimum pitch for each product (asphalt shingles generally need 2:12 or steeper; low-slope membrane systems cover the rest). Roofing subs, framing subs, and GC estimators all work from it, because pitch drives rafter lengths, sheathing and underlayment quantities, fastener patterns, and labor production rates. The classic new-estimator mistake is taking off roof area from the plan view and never applying the slope factor, which understates material and labor on every sloped roof. Two more to watch: assuming one pitch across the whole building when the drawings show different pitches on the main roof and canopies, and missing the steep-slope labor premium most roofing crews charge above roughly 7:12.

How it is measured

Pitch is written as a ratio of rise in inches to a fixed run of 12 inches, such as 4:12, 6:12, or 8:12. Low-slope commercial roofs are called out in fractions of an inch per foot, like 1/4 inch per 12 inches for membrane drainage. Look for it on roof plan slope arrows, section callouts, and the Division 07 roofing specs. To quantify sloped area, convert pitch to a slope factor: take the square root of (rise squared plus 12 squared) and divide by 12. A 4:12 pitch gives a factor of 1.054, 6:12 gives 1.118, and 12:12 gives 1.414. Multiply the flat plan area in square feet by the factor to get true surface area, then add waste for hips, valleys, ridges, and starter courses separately.

Worked example

A worked roof pitch example.

Worked example

The roof plan shows a gable roof with a 2,000 sf footprint at a 6:12 pitch. Step 1, slope factor: square the rise and the run (6 x 6 = 36, 12 x 12 = 144), add them (36 + 144 = 180), take the square root (13.416), and divide by 12 (13.416 / 12 = 1.118). Step 2, sloped area: 2,000 sf x 1.118 = 2,236 sf. Step 3, roofing squares: 2,236 sf / 100 sf per square = 22.4 squares. Step 4, waste: 22.4 squares x 1.10 for 10 percent cutting waste = 24.6 squares, so order 25 squares. At an illustrative installed rate of $450 per square for architectural shingles, the line prices at 25 squares x $450 = $11,250. Skip the slope factor and you would carry 20 squares before waste instead of 22.4 squares; the true area is 11.8 percent larger than the plan area.

How Ruh handles it

How Ruh handles roof pitch.

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Roof pitch: frequently asked questions

What is the difference between roof pitch and roof slope?+

In day-to-day estimating the two terms are used interchangeably, and drawings almost always show rise over a 12 inch run either way. Strictly speaking, slope is rise over run, while pitch is the older carpentry term for rise over total span, so a 6:12 slope on a symmetrical gable was once called a 1/4 pitch. Read the drawing convention, not the label: if the callout shows a number over 12, treat it as rise over run.

How do you convert roof pitch to degrees?+

Divide the rise by the run and take the arctangent. A 4:12 pitch is arctan(4 / 12), about 18.4 degrees; 6:12 is about 26.6 degrees; and 12:12 is exactly 45 degrees. Degrees show up on some metal building and civil drawings, but US roofing specs and labor pricing are organized around the rise per 12 convention, so convert back before you price.

What roof pitch is considered walkable, and why does it matter for pricing?+

Most crews treat roofs up to about 6:12 as walkable, while 7:12 and steeper typically calls for roof jacks, staging, or harness work. That extra handling shows up as a steep-slope labor premium in roofing bids, so an estimator needs to flag the pitch band, not just the area. Many price books carry separate labor rates by pitch range for exactly this reason.

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Related terms

PSF (pounds per square foot)LS (lump sum)EA (each)PSI (pounds per square inch)

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