Are you trying to calculate the pitch of your roof? Wondering how a roofer does it?
A roof’s pitch plays a huge role in so many different things. It’s one of the biggest things a roofer accounts for when estimating any roofing project.
I do not recommend getting on your roof to try to figure it out yourself. However, I also understand wanting to know how it’s done, and some homeowners are handy enough to do it themselves.
So, whether you want to try it out or just want to know how a roofer does it, let’s see it in action.
For over 35 years, Bill Ragan Roofing has taken pride in breaking down all the technical aspects of the roofing industry. Now, I’ll break down the ways you can figure out a roof’s pitch.
By the end of this article, you’ll learn:
- How do you calculate the pitch of a roof?
- How do you measure a roof’s pitch?
How do you calculate the pitch of a roof?
Roof pitch is calculated as a ratio by measuring the number of inches of roof vertically (rise) for every 12 inches it extends horizontally (run). For example, a roof that has 6 inches of rise for every 12 inches of run is a 6/12 pitch.
While pitch is more measured (more on this later) than calculated, people mainly want to figure out the pitch ratio in degrees. To do this, you’ll need to use a bit of trigonometry to figure out the angle of the roof.
Let’s do this using the 6/12 example.
Step one: Divide the roof rise by the roof run
The first step is simply to divide rise by the run. For a 6/12 pitch, that would be 6 divided by 12 to get 0.5.
Step two: Get the arctangent of rise divided by run
For the second step, you’ll need an actual scientific calculator or the version on your phone to find the arctangent and convert it to degrees. I’ll use an iPhone’s scientific calculator for the calculation.
First, you’ll first hit the “2nd” button (or “Shift” on some calculators) to invert “tan” to “arctan” (or “atan”). Next, hit “tan-1” to populate the arctangent and enter the result by dividing the rise by run in the parentheses, 0.5 with our example.
Step three: Get the angle and round up to two decimal places
Finally, hit enter to get the result and round up to two decimal places to get the angle of the roof pitch. For our example, it would be angle = arctan (0.5), which equals 26.57° of roof angle after rounding up to two decimal places.
How do you measure a roof’s pitch?
As I’m sure you noticed, that’s a lot of work just to figure out the angle. While roofing contractors go by pitch more than angle, it’s still good information to have.
However, you can’t do the calculation without first measuring the roof’s pitch. There are multiple ways to measure a roof’s pitch, but some ways are much easier than others.
Using a level and measuring tape on the roof
One of the original ways to measure roof pitch is by using a level and measuring tape to get the rise-over-run. Let’s use a 2-foot level for the example.
On the roof, hold the level horizontally, with one end touching the roof. From the end on the roof, find the 12-inch mark on the 2-foot level.
From the 12-inch mark, use the tape measure to measure the number of inches the level is away from the roof surface. This measurement is called the “rise”, which is the first number of the pitch ratio.
So, if it was 4 inches from the roof surface to the 12-inch mark on the level, the roof has a 4:12 pitch. Unless you feel 100% confident being on a ladder and walking on a roof, I don’t recommend this method to figure out a roof’s pitch.
Measuring the span of the rafters in the attic
If you still want to manually measure the roof pitch without risking your safety, you can do the same thing in the attic. It’s pretty much the same, but instead of using the roof, you’ll use a rafter.
On the underside of the rafter, hold the level horizontally with one end touching the wood. Instead of measuring down, you’ll measure vertically from the 12-inch mark on the level up to the rafter.
This will give you the same rise over run measurements just like if you measured on the roof. However, it comes without the safety risks of being on a roof.
Modern technology and tools
The easiest way to measure a roof’s pitch is by using modern tools and technology. Most roofing contractors nowadays use a pitch gauge or smartphone apps to figure out a roof’s pitch.
These tools work by laying the gauge or smartphone against the roof. For complex roofs with multiple pitches, estimating tools like EagleView are used to get all the measurements for a specific roof.
There are also “pitch cards” with different roof pitches marked on a translucent card. This works by holding the card up from a distance until it overlays the roof to compare to the card to see which angle matches.
How does your roof’s pitch affect your roofing project?
After reading this article, you know how to calculate and measure the pitch of a roof. Even with this information, I don’t recommend getting on your roof to figure out the pitch.
There’s just too much safety risk if you don’t have extensive roofing and ladder experience. On top of this, you’ll learn your roof’s pitch after getting an inspection from a roofing contractor.
So, figuring out the pitch isn’t something you necessarily need to worry about. Instead, it’s important to understand the role your roof’s pitch plays in pricing and other ways.
Check out How Does Roof Pitch Affect the Cost of Your Roof Replacement to learn its impact on your upcoming roofing project.
