What is the difference between roof pitch and roof slope?
Short answer. Technically, slope is rise over run (like 6/12), while pitch is rise over the full span, often written as a fraction (a 6/12 slope is a 1/4 pitch). In everyday roofing, though, people use pitch to mean the x/12 slope, so a roofer saying 6 pitch means 6/12.
The technical definitions
- Slope: vertical rise per unit of horizontal run, written as x in 12. This is what building codes use, for example asphalt shingles requiring a slope of 2 units vertical in 12 horizontal or more.
- Pitch: traditionally, total rise divided by total span (the full width of the building). Because span is twice the run on a symmetrical gable, pitch is half of slope expressed as a fraction.
Old fraction pitches converted
- 1/6 pitch = 4/12 slope
- 1/4 pitch = 6/12 slope
- 1/3 pitch = 8/12 slope
- 5/12 pitch = 10/12 slope
- 1/2 pitch = 12/12 slope (45 degrees)
You may see the fraction style in older carpentry books or historic plans.
How the trades actually talk
Roofers, estimators, insurance adjusters and measurement reports almost always say pitch and mean the x/12 slope. An estimate line like "steep charge, 10/12" or "8 pitch" is a slope value.
Other ways slope is expressed
- Degrees: 6/12 is 26.6 degrees.
- Percent: rise divided by run times 100; 6/12 is 50 percent.
- Ratio: 6/12 can be written 1:2.
For how pitch feeds into roof measurements, see how roofers measure a roof, and for part names, roof anatomy explained.