Roof pitch (slope) tells you how many inches the roof rises for every 12 inches it runs.
For example, 7/12 pitch means that the roof rises 7" for every 12" it runs.
One way to measure is to mark a level at 12" from the top of the roof, hold it perfectly level and measure from the roof surface to your 12" mark. This will give you the rise.
Be careful with this method as a roof with many layers of shingles, or any type of roofing that is irregular can give you less than precise measurement.
Measuring from the bottom of the rafters, the procedure to calculate roof pitch is the same.
This method tends to be more accurate because no layers of roofing are involved.

To use this method there are three possible places to take your measurements:

• 1. The underside of a barge rafter on a gable end.
• 2. The underside of a rafter on a overhang at the bottom of the roof
• 3. The underside of a rafter in the attic.