How to Calculate Roof Pitch: A Step-By-Step Guide

Mar 19, 2023


Moises V.




March 19, 2023


February 2, 2024

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The roof is critical in protecting any structure. Surprisingly, its degree of inclination—known as roof pitch—contributes significantly to its protection.

A well-designed roof pitch enhances a home’s curb appeal and protects it from water damage. It allows rainwater to run off roofs instead of forming ponds. Not to mention it also determines the appropriate type of roofing material that should be used.

You’ll need to know your roof pitch in several contexts. So, read on to find out how to calculate roof pitch and the truth about a popular roofing misconception!

Is the Roof Pitch and Slope the Same Thing?

We’ll begin by dispelling a common misconception about roof pitch. Although “pitch” and “slope” are used interchangeably in roofing, they differ. Thus, measuring a roof’s slope is different from determining its pitch. So let’s quickly explain the distinction. 

When calculating a slope or pitch, you express the roof’s incline as a vertical-to-horizontal ratio. The length of the horizontal part included is the difference between the two measurements. 

Before we get into more detail, familiarize yourself with these three terms:

  • Rise: The vertical distance between the roof’s highest and lowest point.
  • Span: The horizontal distance between opposite ends of the roof.
  • Run: The horizontal distance between the ridge and the roof’s edge.

Measuring the roof pitch involves two variables: the rise and span of the roof. This means you’ll need to measure the entire width of your roof’s base to calculate the pitch.

The slope is the ratio used to express the rise and run of the roof. By now, you know that the run is only a part of the roof’s base, a.k.a; the span.

How Do You Calculate Roof Pitch?

It’s time to review the steps and tools needed to measure your roof pitch.

Tools Required

  • Tape measure
  • Ladder

Measuring Process

There are three simple steps to calculating the pitch; take a look:

Step 1: Select a Measuring Location

The first step in measuring the pitch is deciding whether to take measurements from the roof or the attic. 

If you decide to climb the roof, use caution. Grab a sturdy ladder and give it a quick inspection. Check for any noticeable structural damage or debris buildup that could obstruct your path.

master on repair of roofs makes measurements tool on roof pitch

It goes without saying that you should avoid going up there during rain or snowfall to avoid slipping hazards. Having someone with you while performing this task for added security is also a good idea.

We recommend taking measurements from the attic for several reasons. One of them is that roof coverings like curled shingles can cause inaccurate measurements.

Step 2: Take Measurements

Take out your tape measure once you’ve entered the attic because it’s time to take measurements. We need to take two measurements to calculate the pitch: the span and the rise.

Measure the width or base of the roof from one edge to the opposite edge. Then, measure its height from the ridge to the roof’s base. 

These measurements are easy to obtain from a traditional gable roof or any similar basic structure. However, it’s best to hire a professional if you have a complex roof design, such as a mansard. Calculating the pitch, in this case, will require using special conversion formulas.

Step 3: Calculate the Pitch

Calculating the pitch is a breeze. Simply divide the rise by the span, and you’re done!

For example, if the roof rises 10 feet over a 35-foot span, the pitch is 10/35. Because roof pitch is usually expressed in fractions, it’s often called X over Y.

How Do You Measure Roof Slope?

Knowing your roof’s slope is useful in a variety of situations. For instance, it can tell you whether or not you can apply shingles to your roof. You see, there’s a minimum slope for shingles that, if not met, can lead to water leaks.

That’s why we’d also show you how to measure the slope!

Tools Required

  • Level
  • Marker/Pencil
  • Tape measure

Measuring Process

Like the pitch, you can measure the slope from the roof or attic. We always recommend attic methods for beginners, so we’ll base our process on that.

checking out attic

Step 1: Make a 12-Inch Mark on the Level

When you’re up in the attic, you should first mark your level at 12 inches. That is, of course, if your level is longer than 12 inches; if it’s exactly 12 inches, skip this step.

To explain, when it comes to the slope, we calculate the number of inches the roof rises for every 12 inches it extends horizontally. Therefore, we position the level on one of the roof’s decks and hold it horizontally until it’s perfectly level, serving as our base or run.

Step 2: Measure the Rise

While holding the level against the roof deck, grab your tape to measure the rise. Hold the tape upright at the 12-inch mark you made on the level. The rise is the vertical distance between the start and end of the tape.

Step 3: Calculate the Slope

As mentioned earlier, we define the roof slope as the ratio of rise to run. 

The run is constant because we measure horizontally at a fixed number, 12 inches. So, if you discovered in the previous step that the rise is 6 inches, the slope is 6:12. If the rise is 8 inches, the slope is 8:12, and so on.

Wrapping Up

How to calculate roof pitch is pretty straightforward. That said, knowing the difference between the pitch and slope is critical since each has its own set of applications.

Although taking measures for both formulas isn’t rocket science, leaving it to the professionals is always wise. Doing so will give you more accurate results and save you the trouble of climbing up the roof or attic.

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