Instantly convert Rise and Run into Roof Pitch (X:12), Angle (Degrees), Slope Percentage (%), and Ratio (1:X). Perfect for roofing, ADA ramps, and plumbing drainage.
*Note: Ensure both Rise and Run are in the same unit (e.g., both in inches, or both in feet).
Whether you are framing a roof, pouring a wheelchair ramp, or laying a PVC drain pipe, the fundamental math is exactly the same: Rise over Run.
Simply enter your Rise and Run (in the same unit of measurement, like inches or feet), and the calculator will instantly generate the four universal ways to express that slope.
In carpentry and roofing, slope is almost always expressed as a ratio based on 12 inches of run. This is called "Pitch." If a roof rises 4 inches for every 12 inches of horizontal distance, it is called a 4:12 pitch (spoken as "four in twelve").
| Pitch | Angle (Degrees) | Slope % | Common Use |
|---|---|---|---|
| 2:12 | 9.46° | 16.67% | Low slope / Porches |
| 4:12 | 18.43° | 33.33% | Standard Ranch Home |
| 6:12 | 26.57° | 50.00% | Standard Colonial / Cape Cod |
| 9:12 | 36.87° | 75.00% | Steep / A-Frame Cabins |
| 12:12 | 45.00° | 100.0% | Extreme Steep / Gothic |
If you are building a wheelchair ramp, you must follow the Americans with Disabilities Act (ADA) guidelines. The legal maximum slope for a commercial or public ramp is a 1:12 ratio.
This means for every 1 inch of rise, you must have at least 12 inches (1 foot) of ramp length. If your porch is 24 inches off the ground, your ramp must be at least 24 feet long. In our calculator, a 1:12 ratio will show up as an 8.33% grade and a 4.76° angle.
When laying PVC or ABS drain pipes, gravity is your only engine. If the pipe is too flat, water won't move and solids will clog. If the pipe is too steep, the water will outrun the solids, leaving them behind to cause a blockage.
The universal plumbing code standard for drainage is 1/4 inch of drop per foot of pipe.
If you plug those numbers into our calculator, you will see that standard plumbing slope is exactly a 2% grade and a 1.19° angle.
Mathematically, they are the same concept (Rise over Run). However, the trades use them differently. "Pitch" is used in roofing and is expressed as a fraction of 12 (e.g., 6:12). "Slope" is used in civil engineering, landscaping, and plumbing, and is usually expressed as a percentage (e.g., 2% grade) or a ratio (e.g., 1:12).
Take a 24-inch level and a tape measure. Climb onto the roof (or use a ladder at the gable end). Hold the level perfectly flat against the roof shingles. At the 12-inch mark on the level, measure straight down to the roof shingles. That vertical distance in inches is your pitch. If it measures 5 inches, you have a 5:12 pitch.
A 100% slope does NOT mean a vertical wall. A 100% slope means the Rise and the Run are exactly equal (e.g., 12 inches of rise for every 12 inches of run). This creates a perfect 45-degree angle. A vertical wall is an "infinite" slope.
For standard corrugated or standing seam metal roofing, the absolute minimum pitch is 3:12 (or 1/4:12 for specialized architectural standing seam with sealed seams). If you go lower than 3:12 with standard lap seams, wind-driven rain and capillary action will pull water under the metal panels and cause leaks.