What is Roof Pitch? Roof pitch is the degree of slope to your roof, expressed as a ratio of rise over run - increase in vertical height per unit of length relative to the ground. For example, this diagram shows a 10/12 pitch: What's My Roof Pitch? Here's the easiest way to calculate roof pitch: On both sides of your roof, measure down 36" along the trim from the peak and make a mark. Measure across the face of your gable, from mark to mark, and write down the value in inches. Consult This Roof Pitch Chart: Inches Across Roof...