How Does This Calculator Work?
Slope percentage is calculated as rise divided by run, multiplied by 100 — the same basic ratio as roof pitch, just expressed differently.
Some building codes and drainage specs express roof (or drainage) slope as a percentage rather than the traditional X-in-12 pitch. This calculator gives you that percentage directly.
Example Calculation
Standard Roof Example
A roof rising 6 inches over a 12 inch run.
(6/12)×100 = 50% slope.