A practical example
Convert a 6:12 pitch into an angle
A rise of 6 for a horizontal run of 12 gives an angle of about 26.565°, a 50% slope and a slope factor of about 1.1180. A 4 m horizontal run therefore has a straight slope length of about 4.472 m.
- Choose pitch and enter 6, or enter rise and run using the same units.
- Compare the angle and slope factor, then download the CSV chart if you need a reference.
Straight slope length excludes overhangs and cuts. Geometry alone does not specify a safe roof design or installation.
Back to the toolAbout the roof pitch calculator: instructions and questions
Convert a roof slope between rise per 12 run, degrees and percentage. Add a horizontal run for the rise and straight slope length, then copy the result or download the pitch chart.
How to use the roof pitch calculator
- Choose the value you have. Start with an x:12 slope, an angle in degrees, or measured rise and horizontal run.
- Keep the measurements consistent. Use the same unit for rise and run. Run is horizontal distance, not the length along the sloping roof.
- Keep the conversion. Copy the result, download a text summary or save the reference chart as a CSV file.
A quick reference for common slopes
Roof pitch to degrees chart
Each x:12 value is vertical rise per 12 units of horizontal run. Angles and multipliers are rounded for display; the calculator uses the unrounded values.
| Pitch | Degrees | Slope | Multiplier |
|---|---|---|---|
| 0:12 | 0° | 0% | 1× |
| 1:12 | 4.76° | 8.33% | 1.003466× |
| 2:12 | 9.46° | 16.67% | 1.013794× |
| 3:12 | 14.04° | 25% | 1.030776× |
| 4:12 | 18.43° | 33.33% | 1.054093× |
| 5:12 | 22.62° | 41.67% | 1.083333× |
| 6:12 | 26.57° | 50% | 1.118034× |
| 7:12 | 30.26° | 58.33% | 1.157704× |
| 8:12 | 33.69° | 66.67% | 1.20185× |
| 9:12 | 36.87° | 75% | 1.25× |
| 10:12 | 39.81° | 83.33% | 1.301708× |
| 11:12 | 42.51° | 91.67% | 1.356568× |
| 12:12 | 45° | 100% | 1.414214× |
| 14:12 | 49.4° | 116.67% | 1.536591× |
| 16:12 | 53.13° | 133.33% | 1.666667× |
| 18:12 | 56.31° | 150% | 1.802776× |
| 24:12 | 63.43° | 200% | 2.236068× |
See the working behind the answer
Roof pitch conversion formulas
Let s equal vertical rise divided by horizontal run. Use the same measurement unit for both.
- Rise per 12 runx = 12 × s. A rise of 1.5 m over a run of 3 m gives 6:12.
- Angle in degreesAngle = arctan(s) × 180 ÷ π. At 6:12, the angle is approximately 26.57°.
- Slope percentageSlope % = 100 × s. A 6:12 slope is 50%, not 50 degrees.
- Straight slope lengthLength = run × √(1 + s²). With a 3 m run at 6:12, the straight length is approximately 3.3541 m.
For the distinction between rise/run slope and traditional rise/span pitch, see IKO’s explanation of roof slope terminology ↗. This calculator uses the labelled x:12 rise/run convention.
Roof pitch calculator questions
What does 6:12 roof pitch mean?
In this calculator, 6:12 means 6 units of vertical rise for every 12 units of horizontal run. The ratio is 0.5, giving an angle of about 26.57 degrees and a slope of 50%.
How do I convert roof pitch to degrees?
Divide the rise-per-12 number by 12, then take the inverse tangent and convert the result to degrees. For 6:12, the calculation is arctan(6 ÷ 12), which is approximately 26.57 degrees.
What roof pitch is 30 degrees?
A 30-degree slope has a rise-per-12 value of 12 × tan(30 degrees), approximately 6.93. It is about 6.93:12, with a slope of 57.74%.
Is a 12:12 slope the same as 45 degrees?
Yes. Rise and horizontal run are equal, so the angle is 45 degrees and the slope is 100%. The slope length multiplier is approximately 1.414214.
Is run the same as the full roof span?
No. Run is the horizontal distance for one slope. On a symmetrical gable, it is half the full span. Some technical references use pitch for rise divided by full span; this tool uses the common x:12 rise-over-run convention and labels it explicitly.
Can I enter metric or imperial measurements?
Yes. Use metres, millimetres, centimetres, feet or inches, keeping rise and run in the same unit. Use decimal measurements rather than mixing feet and inches in one field. The unit selector labels your values; it does not convert them.
What does the slope multiplier do?
It multiplies horizontal run to give the straight geometric length along the slope. It equals the square root of one plus the squared rise/run ratio. The calculated length excludes overhangs, ridge adjustments, joints, cuts and material allowances.
Does this calculate a structural rafter size or roofing specification?
No. It converts slope geometry and straight lengths. It does not select structural members, calculate loads, specify roofing materials or determine a permitted minimum slope.
Can I download the roof pitch chart?
Yes. The calculator includes a CSV chart with pitch, degrees, slope percentage and multiplier. You can also copy or download the conversion for your own entered measurements.
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