Quick answer: Slope is rise ÷ run. Multiply by 100 for percent grade, or take the arctangent for the angle. A 6/12 roof pitch equals a 50% slope and about 26.6°.
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.
We keep four separate roof-pitch pages because people arrive with four different questions. If this is not the one you wanted:
A 1 in 12 slope is 4.76° — that is arctan(1÷12). It is also an 8.33% grade, which is the number that matters most often, because 1:12 is the maximum running slope the ADA allows for a wheelchair ramp.
| Ratio | Degrees | Percent grade | Where you see it |
|---|---|---|---|
| 1 in 12 | 4.76° | 8.33% | ADA maximum ramp slope |
| 1 in 16 | 3.58° | 6.25% | Preferred ramp slope, easier to self-propel |
| 1 in 20 | 2.86° | 5.00% | Below this, no handrail required as a ramp |
| 1 in 48 | 1.19° | 2.08% | Maximum cross-slope on an accessible route |
| 1 in 4 | 14.0° | 25% | Steep driveway limit in many jurisdictions |
The three ways of expressing the same slope trip people up constantly. Ratio (1:12) is rise over run. Percent is rise divided by run × 100. Degrees is the arctangent of rise over run. Only percent and ratio are linearly related; degrees is not, which is why a 100% grade is 45° rather than 90°.
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.
Use this reference chart to quickly find the angle and slope for any common roof pitch. Our calculator above gives you exact numbers for custom measurements, but this chart covers the most common residential roof pitches.
| Roof Pitch | Angle (Degrees) | Slope % | Common Use |
|---|---|---|---|
| 1/12 | 4.8° | 8.3% | Flat roof, commercial |
| 2/12 | 9.5° | 16.7% | Minimum for shingles |
| 3/12 | 14.0° | 25.0% | Minimum metal roof |
| 4/12 | 18.4° | 33.3% | Most common residential |
| 5/12 | 22.6° | 41.7% | Traditional ranch style |
| 6/12 | 26.6° | 50.0% | Colonial, Cape Cod |
| 7/12 | 30.3° | 58.3% | Craftsman style |
| 8/12 | 33.7° | 66.7% | Steep traditional |
| 9/12 | 36.9° | 75.0% | Victorian, steep |
| 10/12 | 39.8° | 83.3% | A-frame, chalet |
| 12/12 | 45.0° | 100.0% | A-frame, Gothic revival |
4/12 through 9/12 are the most common residential roof pitches in the United States, with 6/12 being the single most common. These pitches balance aesthetic appeal, attic space, and material cost.
Most asphalt shingle manufacturers require a minimum pitch of 2/12 (9.5°). For pitches between 2/12 and 4/12, special underlayment and installation methods are required to prevent leaks.
Use the formula: degrees = arctan(rise ÷ run). For example, a 6/12 pitch = arctan(6 ÷ 12) = arctan(0.5) = 26.6°. Or just use our calculator above — it converts pitch to degrees instantly.
In heavy snow regions, a minimum 6/12 pitch is recommended to allow snow to slide off rather than accumulate. Steeper pitches like 8/12 through 12/12 are common in mountain and northern regions.
Last reviewed August 2026 · how we source these figures
Every constant this calculator uses and where it comes from, so you can check it rather than take our word for it.
Local codes amend the model IRC and adopt different cycles — your building department governs. Manufacturers revise yields; where your product's data sheet disagrees with a default here, use the product's number. See our full methodology.