A rafter in the attic. The overhang of a rafter at the end of the roof. A barge rafter at the side of the gable.
12 inches is the traditional measurement in the U. S. If you don’t have an imperial ruler, however, you can use any units. Just use the same unit for all measurements, and measure a length at least this size (12 inches / 30 cm).
For example, if you find 4 inches of height with the tape measure at the 12 inch mark on the level, your slope is 4:12 or “4 in 12. " Most people looking for “pitch” are really interested in this measurement. In technical terms, pitch has a different definition. If you’re not sure if you have the right measurement, skip down to find the pitch.
Curled shingles or other non-flat roof coverings make this method less accurate. [3] X Research source Consider measuring from the rake board at the edge of the roof instead. Wear clean, dry, basketball shoes or sneakers with soft soles. These have good traction but are less likely to leave footprints on your roof. [4] X Research source
It may help to lock your tape measure in extended position before you climb. You’ll only need about 12 inches.
If your roof is particularly bumpy, lay down a flat board over the roof first. Place the end of the level against this board. Crouch down or sit, as to minimize the potential for slipping.
In the United States, slopes are traditionally given with 12 as the second number of the ratio. There’s no need to simplify the ratio.
For example, if one side of the roof rises by 8 inches for every 12 inches of horizontal distance, it has a slope of “8 in 12” or “8:12. "
Again, some carpenters and manufacturers use both terms to mean “slope. " Just ask if there’s any confusion about which measurement they’re referring to. For example, if a roof is 32 feet from wall to wall and the ridge is 8 feet above the walls, the pitch has an 8 to 32 pitch, simplifying to “1 to 4” or “1/4”.
For a simple gable roof, the span (wall to wall) will be twice the size of the run (wall to ridge, horizontally). Divide the slope by two to get the pitch. For a roof with the ridge above one wall, the span is the same as the run. The slope is the same as the pitch. For more complex roofs, you may need to calculate it section by section. Carpenters use special conversion charts to estimate the roofing material required based on the slope and shape.
