Roof pitch gets stated four different ways — as a ratio like 6/12, as an angle, as a percentage, and (by everyone who has to order lumber) as a length multiplier. This calculator converts between all four instantly, and the table and guide below explain what each one means, how to measure the pitch of a roof that's already built, and which pitches suit which roofing materials.
Pitch is rise over run, stated per 12 inches of run: a roof that climbs 6 inches for every horizontal foot is 6/12. Degrees is the angle of the slope itself: atan(pitch ÷ 12), so 6/12 = 26.57°. Percent treats the slope as a gradient: pitch ÷ 12 × 100, so 6/12 = 50%. And the multiplier answers the practical question — how much rafter does one foot of run consume? It's √(1 + (pitch ÷ 12)²), so at 6/12 every foot of run needs 1.118 feet of rafter.
Each description has its home turf. Pitch is the language of framing and roofing. Degrees is what drawings, solar installers and your phone's inclinometer speak. Percent belongs to drainage and engineering. The multiplier is the one that reaches your wallet: multiply the run by it and you have the rafter's line length, which is why it appears in every conversion this calculator makes.
| Pitch | Degrees | Percent | Multiplier | Feels like |
|---|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 | Nearly flat |
| 2/12 | 9.5° | 16.7% | 1.014 | Low slope |
| 3/12 | 14.0° | 25% | 1.031 | Low slope |
| 4/12 | 18.4° | 33.3% | 1.054 | Conventional |
| 5/12 | 22.6° | 41.7% | 1.083 | Conventional |
| 6/12 | 26.6° | 50% | 1.118 | Conventional |
| 7/12 | 30.3° | 58.3% | 1.158 | Conventional |
| 8/12 | 33.7° | 66.7% | 1.202 | Conventional |
| 9/12 | 36.9° | 75% | 1.250 | Conventional |
| 10/12 | 39.8° | 83.3% | 1.302 | Steep |
| 11/12 | 42.5° | 91.7% | 1.357 | Steep |
| 12/12 | 45.0° | 100% | 1.414 | Steep |
Going from pitch to degrees is one arctangent; going backwards — from the angle on a drawing to the pitch a framer can lay out — is one tangent. The cards run the three conversions that come up most often: a drawing in degrees, a measured rise and run, and a percent callout on an engineering plan.
A roof drawn at 30° converts to a pitch of 6.93/12. Frame it as 7/12 and the built angle is 30.3° — close enough for roofing, but use degrees for the rafter length if the design depends on it.
Pitch is rise per 12 of run: 9 ÷ 12 of the run gives 9/12 directly. Angle = atan(9 ÷ 12) = 36.87°, percent = 75%, multiplier 1.250.
A plan calling for a 75% roof slope means rise is 75% of run: 0.75 × 12 = 9, so the pitch is 9/12 — the same roof as the previous example, specified the other way.
Manufacturers and codes set minimum pitches because water behaves differently on a shallow slope: wind drives rain uphill under laps, and slow drainage gives it time to find gaps. Asphalt shingles are permitted from 2/12 with doubled underlayment and are standard practice from 4/12; most metal panel systems start at 3/12; clay tile and slate want 4/12 or better. Above 9/12 the constraints flip — the material is happy, but every task on the roof needs staging, and the wall framing below has to resist more outward thrust at the plates.
Pitch also fixes the attic you get. The same 24-foot span gives 6 feet of rise at 6/12 and 12 feet at 12/12 — the difference between a crawl space and a future room. If a conversion above is feeding a build decision, run the resulting pitch through our rafter length calculator to see what it does to rafter lengths and lumber sizes before committing to it.
Once the pitch is settled, the rafter size calculator checks which board may span your roof at that slope, and the span checker verifies a size you already have in mind.
The tape-and-level method in the attic is the most reliable because it samples the framing itself rather than the roofing surface, which can add its own irregularities. Take the measurement at two or three rafters and average them; hand-framed roofs wander by a quarter pitch point between bays. Avoid measuring from a ladder at the eave — the tail and any fascia make the angle there hard to read, and the number you want is the pitch of the roof plane, not of the shingle surface at its edge.
Once you have the pitch, the cut angles follow from it directly — plumb cut, seat cut, hip and cheek angles — and the rafter angle calculator turns your pitch into the full set, with the saw settings to match.
Every result on this page comes from the method described above, using standard framing geometry and the published data credited below. Found a number that looks wrong? Use Report an Error — every report is read.
Pitch is rise over a 12-inch run (6/12 = 6 inches of rise per foot of run). Percent is the same slope as a gradient: rise ÷ run × 100, so 6/12 = 50%. They describe the same roof; pitch is the carpentry unit, percent the engineering one.
About 7/12. tan(30°) × 12 = 6.93, so a 30° roof is a hair under 7/12. Enter 30° in the converter above and it returns 6.93/12 — most framers would frame it as 7/12 and accept the half-degree difference, or work in degrees throughout.
A phone inclinometer gets you close; a level and tape get you exact. In the attic, hold a level horizontally against a rafter, mark 12 inches along the level from the rafter's face, and measure vertically down to the rafter. That vertical figure is the rise per 12 — the pitch.
It depends on the covering: asphalt shingles need at least 2/12 (with double underlayment) and are standard from 4/12 up; metal panels commonly go down to 3/12, standing seam lower; tile and slate want 4/12 or more. Below 2/12 you're in membrane/low-slope territory, not pitched roofing.
Yes — and it's a common source of confusion on older houses, where 'pitch' was stated as rise over the full span rather than over the run. A 'quarter pitch' roof in old terms rises a quarter of the span, which is 6/12 in modern terms. This calculator uses the modern rise-over-run convention throughout.
Yes. Angles, percents and pitches are interchangeable descriptions of slope, so the multiplier — length per unit of run, √(1 + (x/12)²) — applies directly. A 26.57° roof and a 6/12 roof both multiply run by 1.118.
The full common rafter: length, angles, birdsmouth and materials.
Line and cut lengths and angles for the diagonal rafter on a hip roof.
Where two roof planes meet — valley length and its cut angles.
First jack length and the common difference for your spacing.
Single-slope rafters between two different wall heights.
Seat cut, heel height and HAP, checked against the IRC one-quarter limit.
Plumb, seat and cheek angles — plus the saw settings to cut them.
How far a board can span — IRC tables by species, grade and load.
The lumber size a span actually needs. The inverse of the span tool.
Two pitches, one roof — upper and lower rafter lengths.
The full pitch × run table, printable for the workshop wall.
Figure any rafter by hand — formula and framing-square methods.