Roof Pitch Calculator
Enter the rise and run below and this Roof Pitch Calculator converts your measurement into the roof pitch used by builders and roofers, along with the equivalent angle and slope percentage.
Roof Pitch Calculator
Enter the rise and run of your roof to instantly calculate pitch, angle, slope percentage, rafter length, and the roof slope multiplier.
Measure the roof
Use the same unit for both measurements. A 12-inch run is commonly used when describing roof pitch.
Your roof geometry
The diagram and results update automatically as you change the measurements.
Find your roof pitch, angle, slope percentage, and rafter length from a simple rise-and-run measurement.
Trying to figure out whether your roof is 4/12, 6/12, 8/12, or something else? You don’t need to guess from the way the roof looks.
It is useful for homeowners, DIY projects, roof measurements, remodeling estimates, construction planning, and anyone who wants to understand the slope of an existing roof.
What Is Roof Pitch?
Roof pitch describes how steep a roof is.
In the United States and many construction applications, roof pitch is commonly written as X/12, where X represents the vertical rise over 12 inches of horizontal run.
For example:
- 3/12 = 3 inches of rise for every 12 inches of run
- 4/12 = 4 inches of rise for every 12 inches of run
- 6/12 = 6 inches of rise for every 12 inches of run
- 8/12 = 8 inches of rise for every 12 inches of run
- 12/12 = 12 inches of rise for every 12 inches of run
The larger the first number, the steeper the roof.
A 12/12 roof has a 45° angle because its rise and run are equal.
Roof Pitch Is More Than Just a Number
Two roofs can have the same footprint but very different amounts of actual roof surface.
As the pitch increases, the roof surface becomes longer than the horizontal footprint. This matters when estimating roofing materials because shingles, metal panels, underlayment, and other materials cover the sloped roof surface, not simply the area shown on a floor plan.
For example, a 6/12 roof has a slope multiplier of about 1.118. That means the sloped surface is about 11.8% larger than the corresponding horizontal area, before accounting for overhangs, valleys, hips, dormers, and waste.
That is one reason knowing the pitch can be useful before estimating how much roofing material you need.
How to Calculate Roof Pitch
You can calculate roof pitch with a surprisingly small amount of information.
You need two measurements:
Rise: how far the roof goes vertically upward.
Run: the horizontal distance associated with that rise.
The basic relationship is:
Roof slope = Rise ÷ Run
To express that slope as the familiar X/12 roof pitch:
Roof pitch = (Rise ÷ Run) × 12
Example: 8 inches of rise over 12 inches of run
Suppose you measure:
- Rise = 8 inches
- Run = 12 inches
Then:
8 ÷ 12 = 0.6667
So the roof is:
8/12 pitch
The same roof has approximately:
33.69° angle
and:
66.67% slope
The calculator performs these conversions automatically, so you don’t have to work through the trigonometry yourself.
Roof Pitch to Degrees
Roofers and construction documents often describe a roof using pitch, while other situations call for an angle in degrees.
They describe the same slope in different ways.
The conversion is:
Roof angle = arctan(Rise ÷ Run)
Here are several useful reference points:
| Roof Pitch | Approx. Angle | Slope |
|---|---|---|
| 2/12 | 9.46° | 16.67% |
| 3/12 | 14.04° | 25.00% |
| 4/12 | 18.43° | 33.33% |
| 5/12 | 22.62° | 41.67% |
| 6/12 | 26.57° | 50.00% |
| 7/12 | 30.26° | 58.33% |
| 8/12 | 33.69° | 66.67% |
| 9/12 | 36.87° | 75.00% |
| 10/12 | 39.81° | 83.33% |
| 11/12 | 42.51° | 91.67% |
| 12/12 | 45.00° | 100.00% |
These values come directly from the rise/run relationship rather than from an approximation of how the roof looks.
How to Measure It
You do not necessarily need to climb onto the roof to determine its pitch.
One practical method is to work from the accessible underside of the roof, attic framing, or another safe location.
Method 1: Use a level
Place a level horizontally against an accessible rafter or roof framing member.
Mark a horizontal distance, such as 12 inches.
Then measure the vertical distance between that point and the rafter.
For example, if the roof rises 7 inches over a 12-inch horizontal run, the pitch is:
7/12
Method 2: Measure a larger run
You don’t have to measure exactly 12 inches.
Suppose you measure:
Rise = 15 inches
Run = 30 inches
Then:
15 ÷ 30 = 0.5
Multiply by 12:
0.5 × 12 = 6
So the roof is 6/12.
This is useful when a larger measurement is easier to take accurately.
Important measurement tip
Rise and run must use the same unit. You can use inches, centimeters, feet, or another consistent unit; the mathematics is the same.
Roof Pitch vs. Roof Angle vs. Slope
These terms are related, but they aren’t interchangeable.
Roof pitch is normally written as a ratio such as 6/12.
Roof angle expresses the same geometry in degrees, such as 26.57°.
Slope percentage expresses rise divided by run as a percentage. A 6/12 roof has a 50% slope.
So:
6/12 = 26.57° = 50% slope
They describe the same roof, just using different formats.
This distinction becomes particularly useful when comparing information from roofing estimates, architectural drawings, calculators, and building specifications.