Roof Pitch Calculator
Enter rise and run to get roof pitch in X/12, degrees, percent and the pitch multiplier.
Use the same unit for both: in, ft, mm, cm or m.
Horizontal distance from the wall to the centre of the ridge (half the span on a symmetrical gable). Used for the rafter line length.
Line length from the wall plate to the ridge centre line. Excludes overhang/eaves and the ridge-board deduction. This is not a cut length.
What is roof pitch?
Pitch is the inches of rise per 12 inches of run. US and Canadian builders write it as X/12, so 6/12 is said “6 in 12”.
Rise is the vertical height the roof gains. Run is the horizontal distance over which it gains that height. The roof angle is the same slope in degrees from horizontal.
Parts of a roof
- Span
- The full horizontal width between the two supporting walls.
- Wall plate
- The top of the supporting wall, where the rafter sits. Rise and run are measured from here.
- Ridge
- The top line where the two roof slopes meet.
- Rafter
- The sloped member from the wall plate to the ridge.
- Eaves
- The lower edge of the roof.
- Overhang
- The part of the rafter that extends past the wall.
How to measure roof pitch
In the attic, hold a spirit level flat against the underside of a rafter, with one end touching it. Keep clear of roof nails poking through.
Measure 12 in along the level from the touching end and mark it. That is the run.
Measure straight up from the mark to the underside of the rafter. That is the rise: 6 in means a 6/12 pitch.
The 12 in is not fixed. Mark 300 mm along the level instead, measure the rise in mm, and enter both numbers.
Measuring from inside the attic means you never have to climb onto the roof.
Roof pitch chart (1/12 to 12/12)
| Pitch | Angle | Slope % | Multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 |
| 2/12 | 9.46° | 16.7% | 1.014 |
| 3/12 | 14.04° | 25.0% | 1.031 |
| 4/12 | 18.43° | 33.3% | 1.054 |
| 5/12 | 22.62° | 41.7% | 1.083 |
| 6/12 | 26.57° | 50.0% | 1.118 |
| 7/12 | 30.26° | 58.3% | 1.158 |
| 8/12 | 33.69° | 66.7% | 1.202 |
| 9/12 | 36.87° | 75.0% | 1.250 |
| 10/12 | 39.81° | 83.3% | 1.302 |
| 11/12 | 42.51° | 91.7% | 1.357 |
| 12/12 | 45.00° | 100.0% | 1.414 |
How to calculate roof pitch
Rise and run to pitch
Divide rise by run: r = rise ÷ run. Pitch is X = r × 12.
Pitch to degrees
Angle (°) = atan(r) × 180 ÷ π
Percent slope
Slope % = r × 100
Pitch multiplier and rafter length
The multiplier turns a horizontal run into the sloped length: √(1 + r²)
Rafter line length = run × √(1 + r²), the same as √(rise² + run²).
Example: a 6/12 pitch with a 12 ft run length gives a rafter line length of 13.42 ft (13 ft 5 in).
Roof pitch FAQ
Is a 6/12 roof pitch steep?
No. A 6/12 roof pitch is conventional/medium, not steep. As rough categories, not rules: low slope is below about 3/12–4/12, conventional/medium is 4/12–9/12, and steep is above 9/12.
I work in metric. Which result should I use?
Use the angle in degrees or the slope in percent. Metric users usually think in degrees or %, so Metric mode shows those two results largest, at equal weight. For example, a rise of 300 mm over a run of 1000 mm gives 16.70° and 30.0%.