Roof Pitch Chart

How to read a roof pitch chart

A roof described as 6:12, 6/12 or 6 in 12 rises 6 units vertically for every 12 units horizontally. The units cancel: 6 inches over 12 inches and 6 centimeters over 12 centimeters describe the same slope. They do not describe a 6-foot rise over a 12-inch run.

The horizontal distance is the run, not the sloped rafter length. Measuring along the roof and using that measurement as the denominator produces a different ratio and understates the slope. A roof at 12:12 rises one unit for every unit of run, so its angle is 45° and its grade is 100%.

Tradespeople commonly use “roof pitch” for rise divided by run. In traditional geometry, pitch can mean total rise divided by the entire span. For a symmetric gable roof, a 6:12 slope is a traditional quarter-pitch roof because its rise is one quarter of the full span. State the rise:run ratio on an order or drawing to avoid that ambiguity.

Fast check: 4:12 is 18.43°; 6:12 is 26.57°; 8:12 is 33.69°; 12:12 is 45°. A 30° roof is about 6.93:12, not 6:12. The full chart and calculator use horizontal run, never sloped length.

Convert roof pitch to degrees, percent and multiplier

Let r be the rise per 12 units of horizontal run. These are geometric conversions, so they do not depend on roof material, building width or measurement units.

Use degrees for the trigonometric functions when entering an angle into an ordinary calculator. Software functions often use radians; convert degrees by multiplying by π/180 before calling the tangent. The table rounds angles to two decimals and multipliers to four decimals. Use unrounded values when the last fraction of an inch matters.

A 30° roof is approximately 6.928:12, not 6:12. A 45° roof is exactly 12:12. A 50% grade is 6:12, while a 50° roof is approximately 14.301:12. Degrees and percent grade should never be interchanged.

Measure the rise over a horizontal run

Use a drawing or a safely accessible exposed framing surface when possible. Establish a level horizontal reference, measure its horizontal length, then measure the vertical rise over that same distance. Normalize the result to 12: rise per 12 = 12 × measured rise ÷ measured run.

For example, a measured rise of 9 inches over an 18-inch horizontal run gives 12 × 9 ÷ 18 = 6:12. You do not need to measure exactly one foot if a longer baseline gives a clearer reading. Measure the actual roof plane you are checking; a dormer, porch or addition can have a different slope from the main roof.

A digital angle reading can be converted directly with the finder. If you use the underside of a rafter, verify that the measured line is parallel to the roof plane. Ceiling slopes, fascia angles and decorative trim may not be. Small measurement errors matter most when deciding whether a roof meets a material’s minimum slope; avoid rounding a borderline roof upward to qualify it.

Rafter line length and rise: a worked example

Consider a symmetric gable roof with a 24 ft horizontal span and a 6:12 slope. The run from the centerline to one exterior wall is 12 ft. Its geometric rise is 12 × 6/12 = 6 ft. The sloped line from wall reference to ridge reference is 12 × 1.118034 = 13.416 ft, or about 13 ft 5 in.

This is a right-triangle line length, not a finished cut list. Ridge-board or beam details, seat cuts, heel height, bearing locations and measurement conventions change the actual rafter layout. Add the eave projection on the correct basis: a 1 ft horizontal overhang at 6:12 adds 1.118 ft of sloped length. A 1 ft overhang measured along the slope adds exactly 1 ft.

For a shed roof, the horizontal run is normally the full horizontal distance between the relevant high and low references. Do not halve it as you would for one side of a symmetric gable. Hip and valley rafters follow different plan geometry; the common-rafter multiplier alone does not give their cut lengths.

Use the slope multiplier to estimate roof area

For a roof plane with uniform slope, sloped surface area = horizontal projected area × slope multiplier. If the horizontal footprint of both planes of a simple 30 ft × 40 ft gable roof is 1,200 ft² and both planes are 6:12, the geometric roof area is 1,200 × 1.118034 = 1,341.6 ft², before any footprint adjustment for eaves.

Because 1,200 ft² already represents the combined horizontal projection, do not multiply that result by two again. If you measure one side’s horizontal projection instead, calculate that side and add the other planes. For mixed pitches, calculate each plane separately and sum their areas.

Keep waste separate from geometry. Valleys, hips, dormers, starter courses, ridge products, overlap and the chosen roofing system affect ordering. A geometric area of 13.416 roofing squares does not mean an order of exactly 13.416 squares will cover the job. Use the product’s packaging coverage and a project-specific layout allowance.

Low-slope and shingle limits

The conversion chart describes geometry; it does not approve a roofing product. ARMA’s lower-slope shingle guidance allows asphalt shingles from 2:12 to below 4:12 only with special installation procedures and says not to apply shingles below 2:12. Those boundaries correspond to about 9.46° and 18.43°.

GAF Technical Bulletin R-127 likewise identifies 2:12 to under 4:12 as the lower-slope range for its shingle guidance. The exact shingle, underlayment, climate and local requirements still govern the assembly.

Metal roofing is not one universal system: panel profiles, seam details and manufacturer instructions differ. Membrane roofing and drainage design also have their own requirements. A 0:12 entry is included as a mathematical reference and does not mean a roof should be built without drainage. Slope alone also cannot establish whether a roof is safe to walk on.

Boundary note: a roof at exactly 4:12 is outside the 2:12-to-below-4:12 lower-slope shingle range described in the cited ARMA bulletin. Installation instructions still govern. Do not infer safe roof access from a slope label; roof work can require trained professionals and fall protection at any pitch.

Common roof pitch mistakes

Using the full span as the run: for a symmetric gable, the run to the ridge is generally half the span. Treating 12:12 as vertical: it is 45°, while a vertical line has no finite rise:run ratio. Using a 0.5 area factor for 6:12: 0.5 is the slope; the surface-area multiplier is 1.1180.

Applying one pitch to every roof plane: additions and transitions often differ. Calling the multiplier a waste factor: it accounts only for the difference between horizontal projection and sloped length or area. Mixing feet and inches in the ratio: convert both measured lengths to the same unit first.

Roof Pitch Chart FAQ

Sources and data basis

Numeric conversions are independently calculated from the formulas shown on this page. Manufacturer and trade-association references support only the roofing-material guidance; they do not establish rafter sizes, structural capacity or access safety.

• ARMA — Installation of Asphalt Shingles on Lower Sloped RoofsMaterial-specific 2:12 minimum and lower-slope installation guidance.
• GAF — Technical Bulletin R-127Manufacturer guidance for shingles on slopes from 2:12 to under 4:12.
• Turn2Engineering — Roofing CalculatorCompanion material estimator; helps distinguish slope-corrected roof area, waste and packaging.

Reference guidance checked October 27, 2026. The chart is an independent geometry reference; verify current manufacturer instructions and local rules for the specific roofing system.