Understanding your new roof's pitch and slope is incredibly important. This helps you understand how excess water, snow, or debris falls off the roof, which also helps guide you to the right type of shingles or roofing materials you need. We're here to teach you how to easily calculate and estimate your roof pitch angles manually.
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Before calculating the pitch of your roof, let’s go over some basic key terms and measurements so everything is on point.
Rise and run
Rise is the vertical measurement of the distance from one point of your roof to the highest point of the roof. If you look at a right degree angle or a right triangle, you’ll see the rise as the vertical component and the run as the horizontal component.
Run is the horizontal measurement of how far out your roof extends, typically the distance from the peak of your roof to the exterior wall.
Roof slope is often perceived as the same thing as pitch and it's important to understand the subtle difference. Slope is the incline of the roof, and it is represented in a ratio measured in inches of the vertical rise per foot of the horizontal run. For example, a roof with a 4-inch rise for every 12 inches of run, this ratio would look like: 4:12. The ratio always represents inches per foot.
Pitch is the incline of the roof and is instead represented in a fraction dividing the rise by the span, which is the distance between outside walls. For example, a roof with a rise of 4 feet and a span of 24 feet would represent a ⅙ pitch of the roof.
Depending on what type of roof you have, you'll have a different slope ratio or pitch fraction. Let's take a look at some of the main roof types and determine what category your roof falls into.
Flat roofs or low pitch/low slope roofs will typically have a lower ratio and fraction, usually from 1/12-2/12.
More common gable roofs will have a higher slope ratio or fraction from 4/12 to 9/12.
And roofs with a steeper pitch/steep slope, you could see a fraction up to 18/12 or higher.
How to manually calculate your roof pitch
How to calculate your roof pitch on the roof
If you'd like to calculate your pitched roof manually for an exact measurement and aren't afraid of heights, whip out the tape measure and spirit level, and carefully climb the ladder to access your roof. Whether you have an asphalt shingle roof, rubber membrane, or metal roof, always make sure it's safe to stand on your roof first.
Once you're safely on your roof, measure 1-foot up from the base, which will give you the run. Then place the spirit level at the 1-foot marker, and once it is even, measure from the bottom of the level to the top of your roof. This will give you the rise.
For example, if your rise is 6 inches, then your roof pitch will be 6/12. For every 12 inches of horizontal run, the roof rises 6 inches.
How to calculate your roof pitch from inside
An easier way to calculate your roof pitch without going on the roof is to measure the rafter length or truss system in your attic. Place your level under the bottom of the rafter, and after the bubble is in the center, mark it at 12 inches. Then measure vertically from the level to the roof rafter. This measurement will tell you the number of inches your roof rises in 12 inches of run.
Measure your roof’s pitch today
Now that you’re equipped with the proper tools to calculate your roof’s pitch, it’s time to get measuring! Determine the pitch of your roof with our handy guide and find a local roofer to handle your next roofing project today.