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Pitch to angle, slope & rafter factor
Geometry from one number: rise per 12″ of run.
CONSTRUCTION REFERENCE
Roof Pitch Chart
Enter any roof pitch to get the angle in degrees, the slope percent, and the rafter-length factor — plus a printable chart covering every pitch from 1/12 to 18/12.
Pitch is a ratio; everything else is geometry
Roof pitch is written as rise over a 12-inch run: a 6/12 roof climbs 6 inches for every 12 inches across. That single number unlocks the whole triangle — the angle is arctan(rise÷12), the slope percent is rise÷12 × 100, and the rafter-length factor is the hypotenuse per foot of run: √(rise² + 12²) ÷ 12. Enter any pitch above and the calculator runs all three.
A worked example
Take a 6/12 pitch, the most common residential slope in America. Angle = arctan(6÷12) = arctan(0.5) = 26.57°. Slope = 6÷12 × 100 = 50%. Rafter factor = √(36 + 144) ÷ 12 = √180 ÷ 12 = 1.118 — so a 20-foot horizontal run needs 20 × 1.118 = 22.36 ft of rafter (before the ridge cut and overhang). Walkability: comfortable — this is the DIY sweet spot.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Angle | arctan(pitch ÷ 12) | Degrees above horizontal — what a level or phone app reads. |
| Slope percent | pitch ÷ 12 × 100 | Grade in percent — 6/12 is a 50% grade, steeper than any road. |
| Rafter-length factor | √(pitch² + 144) ÷ 12 | Multiply by the horizontal run (ft) to get rafter length (ft). |
| Walkability | OSHA 4:12 steep-slope line | Under ~6/12 most people walk comfortably; past 7/12 bring fall protection. |
Full pitch chart, 1/12 to 18/12
| Pitch | Angle | Slope | Rafter factor | Rise / ft | Walkability |
|---|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | 1″ | Low slope — membrane |
| 2/12 | 9.46° | 16.7% | 1.014 | 2″ | Low slope — membrane |
| 3/12 | 14.04° | 25.0% | 1.031 | 3″ | Walkable with care |
| 4/12 | 18.43° | 33.3% | 1.054 | 4″ | Walkable with care |
| 5/12 | 22.62° | 41.7% | 1.083 | 5″ | Walkable — DIY range |
| 6/12 | 26.57° | 50.0% | 1.118 | 6″ | Walkable — DIY range |
| 7/12 | 30.26° | 58.3% | 1.158 | 7″ | Steep — jacks & harness |
| 8/12 | 33.69° | 66.7% | 1.202 | 8″ | Steep — jacks & harness |
| 9/12 | 36.87° | 75.0% | 1.250 | 9″ | Very steep — pros only |
| 10/12 | 39.81° | 83.3% | 1.302 | 10″ | Very steep — pros only |
| 11/12 | 42.51° | 91.7% | 1.357 | 11″ | Very steep — pros only |
| 12/12 | 45.00° | 100.0% | 1.414 | 12″ | Very steep — pros only |
| 13/12 | 47.29° | 108.3% | 1.474 | 13″ | Very steep — pros only |
| 14/12 | 49.40° | 116.7% | 1.537 | 14″ | Very steep — pros only |
| 15/12 | 51.34° | 125.0% | 1.601 | 15″ | Very steep — pros only |
| 16/12 | 53.13° | 133.3% | 1.667 | 16″ | Very steep — pros only |
| 17/12 | 54.78° | 141.7% | 1.734 | 17″ | Very steep — pros only |
| 18/12 | 56.31° | 150.0% | 1.803 | 18″ | Very steep — pros only |
Who uses this
- Homeowners: translating the roofer's "8/12" into an angle before signing a quote — and knowing whether it is walkable.
- DIYers: the rafter factor sizes lumber and roofing materials from a tape measurement of the run.
- Buyers and inspectors: low-slope roofs (under 3/12) need different materials — a fast pitch check flags the wrong shingle choice.
- Solar shoppers: panel output depends on tilt; the pitch angle is the starting number for the racking math.
Accuracy & limitations
The geometry is exact — these are pure triangle relationships, accurate to the displayed decimals. What the chart cannot know: your local code (some jurisdictions restrict materials below 3/12 or 4/12), the actual pitch of an old roof (measure it — additions and sag lie), and safety (walkability bands are rules of thumb; wet, mossy, or frosty shingles are treacherous at any pitch). This page estimates; structural and safety decisions belong to licensed professionals.
Sizing the access route too? The ramp slope calculator runs the same rise-over-run math for wheelchair ramps, and ramp vs porch lift prices the alternatives.
Cite this calculatorBright Side Kit. “Roof Pitch Chart.” brightoolbox.com, 2026.
Bright Side Kit. "Roof Pitch Chart." https://brightoolbox.com/roof-pitch-chart/ Accessed October 22, 2026.Frequently asked questions
What is a 6/12 roof pitch in degrees?
26.57° — arctan(6÷12). It is also a 50% slope, and each foot of horizontal run needs 1.118 ft of rafter. Enter any pitch on the roof pitch chart above for the full breakdown.
What does 4/12 pitch mean?
The roof rises 4 inches for every 12 inches of horizontal run — an 18.43° angle. It is the OSHA line where roofing officially becomes ‘steep-slope’ work, and the practical floor for standard shingle warranties without special underlayment.
How do I measure my roof pitch?
From inside the attic: hold a level horizontally against a rafter, mark 12 inches along the level, and measure vertically down to the rafter at that mark — the inches are your pitch number. From the ground, a phone inclinometer on the rake board reads the angle; convert it with the chart above.
What roof pitch is walkable?
Most people walk up to about 6/12 comfortably in dry conditions. At 7/12–8/12 bring roof jacks and a harness; past 9/12 leave it to pros. Wet, mossy, or frost-covered shingles are dangerous at any pitch.
How long a rafter do I need?
Multiply the horizontal run in feet by the rafter-length factor from the chart: for a 6/12 pitch over a 20-ft run, 20 × 1.118 = 22.36 ft, before the ridge cut and eave overhang. Add a few percent waste when ordering.
What is the most common roof pitch?
4/12 to 9/12, with 6/12 the single most common on American homes — steep enough to shed water and snow, shallow enough to walk and to keep material costs sane.
Can you put shingles on a 2/12 pitch?
Generally no — standard asphalt shingles are not rated below 2/12 at all, and below 4/12 they need special double underlayment. Low-slope roofs want membrane, built-up, or standing-seam metal instead.