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Free roof pitch calculator. Convert rise and run to pitch, degrees, slope percent, pitch multiplier, and rafter length with an instant reference chart.
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Enter measured project values. Results update only when you choose Calculate.
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Bid a 2,400 SF footprint as 2,400 SF of roof and a 6/12 pitch leaves you 283 SF short — nearly three squares of shingles, underlayment, ice barrier, and the labor to install them, gone before the first bundle hits the deck. The fix is one number: at 6/12 the slope factor is 1.118, so that footprint is really 2,683 SF of roof surface. Every pitch has its own multiplier, and skipping it is the most common way a roofing bid loses money on day one.
This roof pitch calculator earns its keep anywhere the drawings or the measurement source give you plan view instead of surface area: takeoffs from architectural plans, aerial and satellite measurements, and quick drive-by squares counts. It also converts rise-over-run to degrees for saw settings, solar mounts, and drone reports, and flags the thresholds that change the spec — steep-slope labor premiums above roughly 7/12, doubled underlayment between 2/12 and 4/12, and the 2/12 floor below which asphalt shingles are off the table.
Hold a level horizontal, mark 12 inches from the roof (or rafter), and measure straight down to the surface — that vertical distance in inches is your pitch. Measure on the underside of a rafter in the attic or along a rake board when you can: measuring on top of old shingles adds curl and thickness error, and a sagging ridge will lie to you.
Rise-over-run is the trade language; degrees are for saw bevels, solar racking specs, and aerial-measurement reports. The conversion is arctan(rise / 12) — so 4/12 is 18.43 degrees, not 4/12ths of anything. Do not eyeball it: a 2-degree error on a rafter cut compounds across every seat cut on the roof.
Plans, satellite tools, and footprint math all give horizontal projection, and shingles do not install on a projection. Multiply plan area by the slope factor for the measured pitch: 2,400 SF of footprint at 8/12 is 2,400 x 1.202 = 2,885 SF of surface — call it 29 squares before waste, not 24.
Above about 7/12, production drops and harness or staging time goes up, so carry a steep-slope labor premium rather than eating it. Below 4/12, code generally requires doubled or self-adhered underlayment under shingles, and below 2/12 asphalt shingles are prohibited outright — that is a low-slope membrane job at a different unit price. Hips and valleys run longer than they draw: multiply their plan length by the hip/valley factor.
18.43 degrees. The math is arctan(4 / 12) — the angle whose tangent is 0.333. For the neighbors on the table: 3/12 is 14.04 degrees, 5/12 is 22.62, and 6/12 is 26.57.
Measure how many inches the roof rises over 12 inches of horizontal run. Set a level horizontal against the slope, mark 12 inches out, and measure straight down to the surface — 6 inches of drop means a 6/12 pitch. From inside an attic, run the same measurement along a rafter for a cleaner number than measuring over shingles.
6/12 means the roof rises 6 inches for every 12 inches of horizontal run — 26.57 degrees, or a 50 percent grade. It sits in the middle of the common residential range of 4/12 to 9/12: steep enough to shed water fast and take any standard shingle, but still walkable for most crews. Steep-slope labor pricing typically starts a pitch or two above it, around 7/12 to 8/12.
On a jobsite, yes — both mean rise over run, written like 5/12. Strictly speaking, slope is rise per 12 inches of run while pitch was historically rise over the full span (a 6/12 slope on a symmetrical gable is a 1/4 pitch), but almost nobody prices work that way anymore. A slope calculator and a pitch calculator are doing the same arctangent.
Multiply the horizontal (plan) area by the slope factor, which is sqrt(rise^2 + 144) / 12. A 1,800 SF footprint at 5/12 is 1,800 x 1.083 = 1,949 SF of surface; at 10/12 the same footprint is 2,344 SF. The steeper the roof, the more expensive it is to skip this step.
2/12 is the code floor under the IRC — below that, shingles are prohibited and you are into a low-slope membrane system. Between 2/12 and 4/12, code and most manufacturer instructions require doubled underlayment or a self-adhered membrane, which changes both the material list and the labor hours, so confirm the pitch before you price the underlayment line.
Roof pitch describes how steep a roof is. In North American construction, it is expressed as a ratio of vertical rise to horizontal run, normalized to a 12-inch run: a 6/12 pitch means six inches of rise for every 12 inches of run. Roofers, framers, architects, and inspectors all use this notation because it ties directly to material quantities, code compliance, structural calculations, and safety planning. A roof pitch of 4/12 reads as "four in twelve" or "four-twelve" in conversation.
Pitch matters because it changes nearly everything about a roofing job. Steeper roofs have more surface area than the building footprint suggests, requiring more shingles, underlayment, and decking. Steeper roofs also drain faster, accept different shingle types, and require more elaborate fall protection during installation. Pitch determines whether a contractor charges a steep-slope premium (typically anything over 8/12), whether the spec allows three-tab versus architectural shingles, and whether a manufacturer warranty is voided by improper application.
Pitch is also a design language. Low pitches (2/12 to 4/12) read as modern or contemporary. Standard residential pitches (5/12 to 9/12) are traditional ranch, colonial, and craftsman. High pitches (10/12 and steeper) are Tudor, Victorian, and Gothic revival. Architects choose pitch for both function and style, and contractors need to recognize what is being asked for at every stage.
Roof pitch math has three different outputs depending on what you need: the pitch ratio itself, the angle in degrees, and the multiplier used for area calculations. All three start with rise and run.
Pitch = Rise / Run (over 12)
Angle (deg) = arctan(Rise / Run)
Area Multiplier = sqrt(Rise² + Run²) / Run
Worked example: A roof rises 8 inches over 12 inches of run. Pitch = 8/12. Angle = arctan(8/12) = arctan(0.6667) = 33.69 degrees. Area multiplier = sqrt(64 + 144) / 12 = sqrt(208) / 12 = 1.202. So a building with a 1,500 sq ft footprint and an 8/12 roof has 1,500 x 1.202 = 1,803 sq ft of actual roof surface. That same roof presents at about 33.7 degrees, which sets the truss order, the bevel cuts on the rafters, and the soffit return geometry.
Common pitch reference table:
Measuring an existing roof: Hold a 24-inch level horizontally against the roof, with one end touching the surface. Measure vertically from the level to the roof surface at the 12-inch mark. That number is your rise per foot of run. Always measure on a section of straight rafter run, not over a hip or valley, and not on the ridge cap.
4/12 (18.43 degrees) is the threshold pitch for standard asphalt shingle application. Common on mid-century ranch homes, modern minimalist designs, and porches. Drains adequately in moderate climates but not ideal for heavy snow regions. Multiplier 1.054 means roof area is only about 5 percent larger than footprint.
6/12 (26.57 degrees) is the most-built residential pitch in North America. Standard for colonials, craftsman bungalows, and traditional homes. Provides usable attic space, sheds water well, and accepts every shingle product without low-slope underlayment requirements. Multiplier 1.118.
8/12 (33.69 degrees) is where most contractors begin charging a steep-slope premium because productivity drops and roof jacks become required. Common on cape cod, cottage, and pitched-front colonials. Multiplier 1.202 means 20 percent more roof area than footprint.
12/12 (45 degrees) is the standard high pitch for Tudor, Victorian, and Gothic revival architecture. Roof multiplier 1.414, meaning 41 percent more area than footprint and a substantial labor premium. Sheds snow effectively and creates dramatic interior volumes when used over open spaces.
If you measure rise over a 24-inch level, divide by 2. Pitch notation always uses 12 inches of run regardless of how you measured.
A homeowner saying "normal pitch" might mean 8/12, which carries a 30 percent labor premium. Always measure or pull the spec.
Slopes between 2/12 and 4/12 require a double-layer underlayment or self-adhered membrane under shingles. Quote it correctly or risk warranty issues.
Slope percentage (rise / run x 100) is used in commercial low-slope work. Pitch is the residential ratio. A 50 percent slope equals a 6/12 pitch.
Footprint area times pitch multiplier equals true roof surface. Skipping this step under-orders shingles by 5-40 percent depending on pitch.
Older homes often have shed dormers or additions at different pitches. Measure each plane separately and apply the matching multiplier.
Production field guide
Roof pitch is the slope of the roof expressed as a ratio of vertical rise to horizontal run, typically over a 12-inch run. A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance. Pitch is the most common way North American roofers and contractors describe slope because it ties directly to material quantity calculations, drainage characteristics, and building code requirements. Steeper pitches shed water and snow faster, but cost more to install due to safety equipment and slower productivity.
Measure the vertical rise and horizontal run, then express as rise/run normalized to 12 inches. If you measure a 4 inch rise over a 12 inch run, the pitch is 4/12. If you measure a 5 inch rise over a 10 inch run, normalize: rise per 12 inches of run = 5 x (12/10) = 6 inches, so the pitch is 6/12. The most accurate measurement uses a level at least 24 inches long held horizontally against the roof, then a tape from the level to the roof surface at the 12 inch mark.
Pitch ratio converts to degrees using arctangent: angle = arctan(rise / run). For 6/12, angle = arctan(6/12) = arctan(0.5) = 26.57 degrees. Common conversions: 3/12 = 14.04 deg, 4/12 = 18.43 deg, 5/12 = 22.62 deg, 6/12 = 26.57 deg, 7/12 = 30.26 deg, 8/12 = 33.69 deg, 9/12 = 36.87 deg, 10/12 = 39.81 deg, 12/12 = 45 deg. Knowing the angle is useful for setting saw bevels, ordering pre-pitched trusses, and confirming code compliance.
A 6/12 pitch equals 26.57 degrees, or about 26.5 degrees rounded. The percentage slope is 50 percent (rise of 6 over run of 12 = 0.5 = 50 percent). Six in twelve is the most common residential pitch in North America because it sheds water well, provides usable attic space, and balances installation cost against weather performance. It is also the dividing line where many manufacturers switch from low-slope underlayment requirements to standard application.
The pitch multiplier converts a building footprint area into actual roof surface area. The formula is sqrt(rise squared + run squared) divided by run. For 6/12, multiplier = sqrt(36 + 144) / 12 = sqrt(180) / 12 = 1.118. Common multipliers: 4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 9/12 = 1.250, 10/12 = 1.302, 12/12 = 1.414. Multiply your footprint by the matching factor to get the true roof area before calculating shingles, underlayment, and decking.
Rafter length depends on pitch and run. The unit length per foot of run equals sqrt(1 + (rise/12) squared) x 12 inches. For 6/12 pitch, unit length = sqrt(1 + 0.25) x 12 = 13.42 inches per foot of run. For a 14 foot run, the rafter length to the ridge is 14 x 13.42 / 12 = 15.66 feet, or about 15 feet 8 inches. Add the overhang and tail cut as needed. Most rafter tables in framing references express this as "unit run rafter length" for each common pitch.
Standard asphalt shingles are rated for slopes of 4/12 (18.43 degrees) and steeper using normal application methods. Between 2/12 and 4/12, shingles can be installed using a low-slope underlayment system with a double layer of underlayment or a self-adhered membrane underneath. Below 2/12, shingles are not appropriate; the roof needs a low-slope or flat-roof system such as TPO, EPDM, modified bitumen, or built-up roofing. Always confirm with the shingle manufacturer specs before bidding.
Most residential roofs top out at 12/12 (45 degrees), but architectural styles such as Victorian, Tudor, and Mansard can run 16/12 (53.13 deg), 18/12 (56.31 deg), or even 24/12 (63.43 deg). Anything over 8/12 is considered steep slope and requires roof jacks, harnesses, and slower installation pace. Code requirements for snow loads, wind uplift, and drainage all relax as pitch increases past 12/12 because the geometry naturally sheds load and water.
Roof pitch is rise over run. The run is always 12 inches in standard pitch notation. Rise is the vertical distance the roof goes up over that 12 inches. Decide whether you have a target pitch already (e.g., spec calls for 6/12) or you are measuring an existing roof.
Hold a 24-inch level horizontally against the roof at the 12-inch mark. Measure straight down from the end of the level to the roof surface. That measurement, divided by 2 (because you are working over 24 inches not 12), is the rise per foot of run. A 12 inch drop over 24 inches equals a 6/12 pitch.
Take arctangent of (rise / 12). Many calculators have an arctan or atan function. For 6/12, atan(0.5) = 26.57 degrees. Use the angle for saw bevel settings, truss orders, and any documents that require degrees rather than ratio.
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This calculator solves one bounded formula from the inputs shown. BuildVision AI supports reviewed plan takeoff, complete-document CSV, and editable quote lines; the estimator owns pricing and final bid approval.