Roof Pitch Calculator

Common Roof Pitch Chart (4/12, 6/12, 8/12, etc.)

This roof pitch angles chart covers the pitches used on almost every North American home — from the 1/12 drainage minimum up through the 12/12 45° breakover and the steep 14, 16, and 18/12 family found on Gothic and Mansard roofs. Use it to look up a single value (for example, the 5 12 roof pitch at 22.62° or the 6 12 pitch degrees at 26.57°) or to compare pitches side by side when choosing a roof slope for a new build.

Angles computed with degrees = atan(X/12) × 180/π and rounded to two decimals. Slope% = (X/12) × 100.

Spotlight: 14 12 Roof Pitch and the Steep-Pitch Family

The 14 12 roof pitch (49.40°, slope 116.67%) is the first entry in the steep family shown in this roof pitch angle chart and it sits well past the 8/12 (~33.7°) walkable ceiling. As a roofing pitch chart rule of thumb, every step up in the steep family (12 → 14 → 16 → 18) adds roughly 3° to 4° of angle and pushes the slope percent up by about 17 points per step: 12/12 is 45°/100%, 14/12 is 49.40°/116.67%, 16/12 is 53.13°/133.33%, and 18/12 is 56.31°/150%. Because slope exceeds 100% past 12/12, the rafter is rising faster than it runs horizontally — which is exactly why Gothic, A-frame, Mansard, and chalet designs use these pitches to make the roof plane a visible architectural feature rather than a sheltering skin.

On a 14/12 pitch, every foot of horizontal run needs about 18.44 inches of rafter length along the slope (12 × √(1 + (14/12)²) ≈ 18.44), versus 16.97 inches for a 12/12 and just 13.42 inches for a 6/12. That extra length drives lumber depth (deeper rafters resist the longer unbraced span) and material cost — for the same square footage of footprint, a 14/12 roof uses roughly 37% more sheathing and shingles than a 6/12 roof. When you read a value off this roof pitch angle chart, plug it into the interactive roof pitch slope calculator above (Mode B) to confirm the angle and slope percent before ordering material, and consult the rafter length and rafter lumber size calculators (linked below) for the actual stock dimensions.

Spotlight: 4 12 and 5 on 12 Roof Pitch — the Residential Workhorses

The 4 12 pitch roof (18.43°, slope 33.33%) and the 5 on 12 roof pitch(22.62°, slope 41.67%) are the two most common shallow residential slopes in North America. Both sit well within the walkable range, which is why builders default to them for ranch homes, porches, garages, and sheds. A 4/12 is the minimum pitch most asphalt-shingle manufacturers will warranty without an ice-and-water membrane, while a 5/12 is steep enough to shed snow and water confidently in most climates without approaching the 8/12 fall-protection threshold.

When you use this page as a 4 12 pitch roof calculator or a 5 on 12 roof pitch calculator, Mode B returns the full set of derived values instantly: the angle in degrees, the slope percent, and the plumb-cut and seat-cut angles for marking the rafter. For 4/12 that is 18.43° plumb / 71.57° seat; for 5/12 it is 22.62° plumb / 67.38° seat. The rafter length per foot of run is 12 × √(1 + (X/12)²) — about 12.65 inches for 4/12 and 12.53 inches for 5/12 — which means a 10-foot run needs roughly 10′ 6″ of rafter stock at either pitch. For the full rafter length (including overhang and birdsmouth), switch to the dedicated rafter length calculator linked below.

Spotlight: 6 12 Pitch Roof — the North American Standard

The 6 12 pitch roof (26.57°, slope 50.00%) is the single most common residential roof pitch in North America, and for good reason. It is the steepest pitch that remains comfortably walkable for an experienced roofer in dry conditions without fall protection, which keeps installation and maintenance costs down. At the same time, 26.57° is steep enough to shed rain and light snow efficiently across every climate zone from the Pacific Northwest to the Mid-Atlantic. A 6 12 roof pitch calculator — enter 6 in Mode B above — returns 26.57°, a 50% slope, and plumb-cut / seat-cut angles of 26.57° / 63.43° for rafter layout. The rafter length per foot of run is 12 × √(1 + (6/12)²) ≈ 13.42 inches, so a 12-foot run needs about 13′ 5″ of rafter stock. Builders and architects default to 6/12 because it balances headroom, water shedding, walkability, and material cost — it is the “if you don’t know, use 6/12” pitch.

Spotlight: 8 12 Pitch Roof — the Walkability Threshold

The 8 12 pitch roof (33.69°, slope 66.67%) sits right at the boundary between walkable and steep-slope roofing. At 33.69° the roof plane is steep enough that OSHA-style fall protection — harness, anchor, and a competent person — becomes mandatory for anyone working on it, which is why 8/12 is often cited as the fall-protection threshold. Pitches at or above 8/12 also shed heavy snow rapidly, making them popular in mountain and lake-effect snow regions. An 8 12 pitch calculator (enter 8 in Mode B) returns 33.69°, 66.67% slope, and plumb / seat cuts of 33.69° / 56.31°. The rafter length per foot of run is 12 × √(1 + (8/12)²) ≈ 14.42 inches — about 7% more lumber per foot of run than a 6/12, which compounds across a full roof. Choose 8/12 when the climate demands aggressive snow shedding or the architectural style calls for a visually prominent roof plane; choose 6/12 when walkability and economy matter more.

Spotlight: 12 12 Pitch Roof — the 45-Degree Breakover

The 12 12 pitch roof (45.00°, slope 100.00%) is the geometric breakover where rise equals run — the roof climbs one inch for every inch it spans horizontally. At exactly 45° the plumb cut and seat cut angles are mirror images (both 45°), the slope percentage hits 100%, and the rafter length per foot of run is 12 × √2 ≈ 16.97 inches. A 12/12 is never walkable without scaffolding or roof jacks; it is the domain of Gothic, Tudor, chalet, and French Eclectic designs where the roof plane is a primary architectural feature. Because the rafter is rising as fast as it runs, a 12/12 roof uses roughly 26% more sheathing and shingles than a 6/12 over the same footprint, and the interior attic volume is generous — often enough for a full second floor. Use the 12 12 pitch calculator above (enter 12 in Mode B) to confirm the 45° angle and the matching plumb / seat cuts before ordering material or setting the saw bevel.

Rafter Angle Calculator: Plumb Cut and Seat Cut from Pitch

The roof pitch angle computed above is also the rafter angle you set on your saw when cutting the rafter’s plumb cut. The plumb cut — the vertical face at the ridge, where the rafter meets the ridge board — is set to the pitch angle itself: degrees = atan(X/12) × 180/π, so a 6/12 rafter is plumb-cut at 26.57°. The seat cut — the horizontal notch on the birdsmouth that bears on the top plate — is the complement: 90° minus the pitch angle, so the same 6/12 rafter is seat-cut at 90° − 26.57° = 63.43°. Because plumb cut = pitch angle, a single rafter angle calculator input (the X/12 pitch) gives you both saw settings at once, which is why the interactive tool at the top of this page doubles as a roof pitch angle calculator for carpenters laying out rafters.

Plumb-cut angle = pitch angle = atan(X/12) × 180/π. Seat-cut angle = 90° − plumb-cut angle. At 12/12 both cuts are 45° because rise equals run, so the plumb and seat cuts become mirror images.

Two cautions when transferring these angles to lumber. First, the plumb cut on a circular saw is set by tilting the blade to the pitch angle (e.g. 26.57° for a 6/12 rafter); the saw’s bevel scale reads that angle directly, so the pitch angle is the saw setting. Second, the birdsmouth seat cut is sometimes laid out with a framing square using the complementary angle because the square rests on the bottom edge of the rafter rather than the plumb line — confirm which reference your square uses before cutting. Use this page as a roof pitch angle calculator to read the plumb cut, then subtract from 90° to derive the seat cut. For the actual rafter length along the slope (the hypotenuse) and the correct lumber size for that span, use the rafter length calculator and the rafter lumber size calculator — both consume the same pitch angle computed here.

How to Measure Roof Pitch on an Existing Roof

The comparison matrix at the top of this page ranks four field methods. The Best Practice — the inside-attic level-and-tape method — wins on safety and accuracy because you never leave the floor and you measure against a rafter’s true plumb face. The steps below walk through that method end-to-end, so you can work out roof pitch and convert it to degrees without climbing a ladder.

1. 1
   ☑ CheckpointEnter the attic and locate a rafter that bears on the exterior wall plate. Identify its plumb (vertical) face — the bottom edge of a common rafter is already plumb-cut relative to the roof slope.
2. 2
   ☑ CheckpointHold a 24-inch or longer spirit level against the bottom edge of the rafter, bubble centered, so the level is truly horizontal.
3. 3
   ☑ CheckpointFrom a chosen starting point on the rafter, measure exactly 12 inches horizontally along the level and mark that point on the level with a pencil.
4. 4
   ☑ CheckpointFrom that 12-inch mark, measure straight up (perpendicular to the level) to the underside of the rafter. Record the distance in inches to the nearest 1/16 inch.
5. 5
   ☑ CheckpointThat vertical measurement is the rise for a 12-inch run — your X value in the X/12 pitch expression. A 6-inch reading means a 6/12 pitch.
6. 6
   ☑ CheckpointRepeat on a second rafter 4 feet away. If the two readings differ by more than 1/16 inch, the roof is framed inconsistently; average the two and note the deviation for the contractor.

Once you have the X value, plug it into the interactive roof slope calculator online above (Mode B) to get the angle and slope percentage instantly. That answers both how to determine pitch on a roof and how to determine roof slope in a single pass: the level-and-tape step gives you the rise, and the calculator converts it into every other unit you need for ordering shingles, sizing rafters, or scheduling the roofer.

How to Work Out Pitch — Other Methods and Reverse Conversion

The level-and-tape steps above cover the safest attic method, but you can also work out pitch from three other starting points. From the angle in degrees — a smartphone clinometer reading, a stamped truss spec, or a builder’s drawing — reverse the formula: X = 12 × tan(angle), so a 30° roof gives X = 12 × tan(30°) = 6.93, i.e. roughly a 7/12 pitch. From a speed square at the rake board, rest the square’s lip against the bottom of the rake and pivot until the hypotenuse aligns with the slope; the pivot mark on the commons scale reads the pitch directly in X/12 form (a “6” on a Swanson-style square is a 6/12). From a smartphone clinometer app, lay the phone flat against the underside of a rafter plumb cut and read the angle, then convert with X = 12 × tan(angle) — but treat it as a ballpark, since uncalibrated sensors drift ±2–3°.

Whichever method you use, type the result into the roof pitch slope calculator above — Mode A for a rise-and-run pair, Mode B for an X/12 value — and it returns the angle, slope percent, and X/12 in one pass. That makes the same tool act as a calculator roof pitch specialist (enter an X/12 in Mode B to read every other unit), a roof calculator pitch lookup (enter a rise and run in Mode A from raw measurements), and a roof pitch angle calculator simultaneously: one input, every unit a framer, roofer, or inspector needs.

Flat Roof Slope Calculator: Minimum Pitch for Low-Slope Roofs

A flat roof slope calculator answers a deceptively important question: even a “flat” roof is not truly flat — it needs a minimum slope to drain water off the surface before ponding causes leaks or structural overload. Building codes and membrane manufacturers require a minimum roof pitch of 1/12 (4.76°, 8.33% slope) for most flat-roof membranes (TPO, EPDM, modified bitumen, built-up). Below 1/12, standing water accumulates, the membrane degrades prematurely, and the dead-load deflection can create a ponding instability loop where each inch of water weighs 5.2 psf and further deflects the structure.

To use this page as a flat roof slope calculator, enter 1 in the X/12 input (Mode B) and the tool returns 4.76° and 8.33% slope — the drainage minimum. For tapered-insulation designs that slope toward roof drains or scuppers, common targets are 1/12 to 2/12(4.76°–9.46°); for a coal-tar pitch roof that relies on gravel ballast, 1/12 is typical. The following table summarizes the minimum slope requirements by roof covering so you can confirm your flat-roof design meets both code and the manufacturer’s warranty.

Minimum slopes per IRC R905 and manufacturer warranty specs. A construction slope calculator for flat roofs must confirm the as-built slope accounts for deflection: a nominally 1/12 design can drop to 0.5/12 at midspan under load, so always oversize the tapered insulation slope at the drain by 50%.

For the full rafter layout on a low-slope or shed roof, the Shed Roof Rafter Calculator guide walks through single-slope framing end to end, including the birdsmouth, overhang, and minimum pitch considerations specific to shed and lean-to roofs.

Rise and Run Calculator: How to Calculate Roof Pitch from Measurements

A rise and run calculator for roof pitch takes the two numbers you measure on site — the vertical rise and the horizontal run — and returns the pitch in every unit a framer, roofer, or inspector needs. The interactive calculator at the top of this page (Mode A) is exactly that: enter your measured rise and run in inches and it outputs the X/12 pitch, the angle in degrees, and the slope percentage in real time. The underlying formula is the arctangent:degrees = atan(rise / run) × 180/π, withX/12 = (rise / run) × 12 andslope% = (rise / run) × 100.

The key to figuring roof slope from a rise-and-run pair is measuring the run horizontally, not along the rafter. The most common error is measuring along the slope (the hypotenuse) instead of horizontally — that inflates the run and understates the pitch. Use a 24-inch level against the rafter’s bottom edge, mark 12 inches along the level (the run), then measure straight up from that mark to the rafter (the rise). The rise in inches over that 12-inch horizontal run is your X value, so a 5-inch rise over a 12-inch run is a 5/12 pitch (22.62°, 41.67% slope). The roof pitch calculator above applies this directly: a rise of 6 and a run of 12 returns 6/12, 26.57°, and 50.00%.

Once you have the pitch from your rise-and-run measurement, the same value feeds every downstream calculation: the rafter length (Pythagorean theorem on the same rise and run), the plumb-cut angle (equal to the pitch angle), and the lumber size (from the span tables). To figure out roof pitch from any starting point — rise and run, an X/12 value, or an angle in degrees — use whichever input mode matches what you have; the calculator converts between all three because they describe one geometry.

Roof Slope Percentage Conversion & Pitch Conversion Chart

A roof slope conversion chart translates between the three notations every trade uses for the same roof: X/12 pitch (carpenters), slope percentage (building codes and drainage specs), and angle in degrees (saw bevels and speed squares). The full roof pitch conversion chart below covers 1/12 through 24/12 — the complete range from flat-roof drainage minimum to near-vertical steeple pitch — with the angle, slope percent, and the rafter length multiplier (the ratio of rafter length to horizontal run). Use this roof pitch degrees chart to look up any pitch in one pass, or verify a single value with the interactive calculator above.

Rafter multiplier = √(1 + (X/12)²); multiply by the horizontal run (in feet) to get the rafter length along the slope. Angle = atan(X/12) × 180/π. Slope% = (X/12) × 100. The full 1/12–24/12 chart is in the Common Roof Pitch Chart section above.

To convert in the reverse direction — from slope percentage back to X/12 pitch — useX = 12 × (slope% / 100). A 50% slope is 12 × 0.50 = 6, giving a 6/12 pitch. From degrees back to X/12, useX = 12 × tan(angle). The degree to pitch calculator built into this page handles both reverse conversions automatically: enter any value in Mode B and the tool returns the angle and slope percent, or work backward from a known angle using the tan formula. This makes the same tool a pitch to degrees converter, a pitch degree calculator, and a degree to pitch calculator in a single input.

Shed Roof Pitch Calculator Guide

Calculating roof pitch for a shed follows the same rise-over-run method as any other roof, but shed roofs are almost always single-slope (a “lean-to” or “skillion”), which simplifies the geometry: one plane, one pitch, one rafter length. The typical shed roof pitch ranges from 3/12 to 6/12 (14.04°–26.57°). Below 3/12 and most shingle warranties require an ice-and-water membrane; above 6/12 the shed walls need to be tall enough that the high-side wall becomes structurally awkward. A shed roof pitch calculator — use Mode B above — lets you enter the X/12 value and instantly read the angle, slope percent, and plumb / seat-cut angles for the shed rafters.

To calculate roof pitch for a shed from scratch, you need two numbers: the difference in wall heights (the rise) and the shed depth (the run). For example, a 10-foot-deep shed with an 8-foot front wall and a 6-foot back wall has a 2-foot rise over a 10-foot run. Convert to inches per foot: 24 inches ÷ 10 = 2.4 inches per foot, so X = 2.4 × 1 = 2.4, giving a roughly 2.4/12 pitch (11.31°). Enter 2.4 in Mode B above to confirm the angle and slope percent, then size the rafter with the Rafter Lumber Size Calculator and cut it to length with the Shed Roof Rafter Calculator guide, which walks through the full lean-to rafter layout including birdsmouth and overhang.

The roofing pitch calculator on this page works identically for shed roofs and houses: pitch is pitch, regardless of building size. What changes for a shed is the rafter size (typically 2x4 or 2x6 vs 2x8+ for a house) and the framing complexity (single-slope vs gable or hip). For the complete shed rafter cut list — length, birdsmouth, plumb cut, seat cut, and overhang — the dedicated shed guide linked above carries the full walkthrough.

Degree to Pitch Calculator: Converting Angles Back to X/12

A degree to pitch calculator does the reverse of the standard pitch-to-degrees conversion: given an angle in degrees, it returns the X/12 pitch and the slope percentage. The formula is X = 12 × tan(angle), where tan is the tangent function. For a 30° roof: X = 12 × tan(30°) = 12 × 0.5774 = 6.93, which is roughly a 7/12 pitch (30.26°). For a 45° roof: X = 12 × tan(45°) = 12 × 1.0 = 12, confirming the 12/12 = 45° identity. The interactive pitch angle calculator above handles this reverse conversion in Mode B: enter the X value that corresponds to your angle and read the result, or use the tan formula to find X from a known degree value.

This reverse conversion matters when a roof angle comes from a non-pitch source — a smartphone clinometer reading, a stamped truss spec sheet, an architectural drawing that lists the roof in degrees, or a speed-square setting. Converting that angle back to the X/12 pitch lets you look up the rafter length multiplier, the plumb-cut angle, and the correct span-table row. The roof pitch to angle chart in the Common Roof Pitch Chart section above lists every standard pitch with its degree equivalent, so you can also find the X/12 by scanning the angle column rather than computing the tangent.