How to use this roof pitch chart
Read across a row to see the same slope in three forms. The rafter factor converts a horizontal run into a theoretical diagonal length. Select the pitch in the first column to open the roof pitch calculator with that value already entered.
The chart uses x:12 notation, where x is the rise for every 12 horizontal units. This ratio works equally in imperial and metric measurements. A 6:12 roof rises 150 mm over a 300 mm run, just as it rises 6 inches over a 12-inch run.
Example: a 6:12 roof with a 10-foot run
The factor for 6:12 is approximately 1.1180. Multiplying a 10-foot horizontal run by the unrounded factor gives 11.1803 feet of theoretical sloped length. With a 3-meter run, the same calculation gives 3.3541 meters.
For an overhang, use the rafter calculator, where the overhang input is horizontal. The table does not include ridge-board deductions, birdsmouth depth or cutting allowances.
The formulas behind the table
- Slope ratio = pitch ÷ 12.
- Angle in degrees = arctan(slope ratio) × 180 ÷ π.
- Slope percent = slope ratio × 100.
- Rafter factor = √(1 + slope ratio²).
Displayed factors are rounded to four decimal places. Keep unrounded values when you need a more precise result; entering your dimensions in the calculator does this automatically. Percent is not degrees: a 100% slope is 45°, while a 50% slope is approximately 26.57°.
Check the measurement first
The run follows a horizontal line, not the rafter itself. See the run versus rafter length diagram if your tape measurement was taken along a sloping board. To measure an existing slope, use the roof pitch measuring guide.
This is a geometry reference. It does not select roofing materials, determine drainage requirements or assess structural capacity. Read our calculation methods or report a correction.