How to calculate roof pitch length?

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Whether you’re looking to take the plunge of a new roofing project, or are trying to frame the roof yourself; you’d be interested to know how to calculate roof pitch length?

So, say goodbye to guesswork and hello to accurate roof pitch calculations with our expert tips below:

Know the basics

If you’re a newbie, you might not even understand the basic terms like pitch, rise, run, apex, and rafter length. So, let’s start with the basics to help you completely understand and master the art of calculating the roof pitch.

If you further want to know the details how to measure the roof pitch, here’s a detail guide I’ve made for that purpose.

What’s the pitched roof? A pitched roof is a roof that has two or more sides that come together at a peak at the top of the structure. This type of roof is commonly found in most homes in Britain, where two sets of rafters meet at the top, also known as the apex or ridge. Pitched roofs come in various shapes and sizes, from simple to complex designs.

What is run of a roof? Run is the horizontal length between the peak of the roof and the wall.

The first one is the “run”, which is the horizontal distance the rafter covers. It is measured from the center line of the rafter to the center of the ridge board or whatever the rafter is attached to. The run is simply half the span of the roof. Note that the overhang is a separate measurement and should not be included in the run measurement.

What is rise of a roof? Rise is the height of the apex above the structure wall. The rise in a roof refers to the vertical distance from the top of the eaves (the lower edge of the roof) to the peak of the roof. In a sloped roof, the rise is measured on a line that is perpendicular to the rafters, also known as the plumb line.

The rise is important because it determines the slope or pitch of the roof, which affects the aesthetic of the building and the effectiveness of the roof in shedding water and snow.

What is pitch of the roof? Pitch of roof is the ratio of the rise to the run. For example a roof with pitch of 4 in 12 means that for every 12 inches of horizontal run, the roof rises 4 inches.

Roof pitch = (1/(tangent (rise/run)) x 180/ π

Mastering the Art of Roof Pitch Calculation: A Step-by-Step Guide for DIYers

Calculating the pitch of your roof is important for a variety of home projects, particularly if you’re planning to replace or install a new roof covering or window. To calculate the pitch of your roof, you’ll need a measuring tape, a spirit level, and a calculator.

To make things simple, I’ve tried to explain the calculation separately for degrees or a in a ratio format like H:V.

Calculating roof pitch in degrees

One way to calculate the roof pitch is in degrees. To do this, you’ll first need to measure the run and rise of the roof.

  • You can use the measuring tape or meter tap and a spirit level. Just try to note the horizontal length or the span between the center of the roof i.e. peak to the edge of the wall.
  • On the other hand, the rise will be the height of the apex above the structural wall.
  • Now you simply have to divide the rise by run and that will be the tangent of the roof. So, tangent = rise / run.
  • Now you can calculate the roof pitch using formula below:
  • Roof pitch = (1/(tangent (rise/run)) x 180/ π


Let’s say we have a roof with rise of 9 meters and run of 5.5 meters. Here’s how we can calculate the pitch of the roof:

  • Step 1: Calculate the tangent of the rise/run ratio:
    • Tangent (rise/run) = tangent (9/5.5)
  • Step 2: Calculate the inverse of the tangent value:
    • 1/ tangent (9/5.5) = 0.72
  • Step 3: Multiply the result from step 2 by 180/π
    • 0.72 x (180/π) = 26.56

So, the roof pitch is approximately 26.56 degrees.

Note: The result is an approximation, because the formula is a simplification of the more complex trigonometric calculations and the final result should be rounded to the nearest degree.

Calculating roof pitch in ratios

Another way to calculate the pitch of your roof is as a ratio like X:12. That means we will see that how much a roof will rise for every 12 inches of horizontal distance (run).

  • To do this, place one end of the spirit level against the roof deck.
  • Mark the point at 12 inches along the level that’d be your run.
  • Now, measure the distance between the top of the spirit level at the mark and the roof deck. This’d be your rise.
  • Now you can express the roof pitch as x:12 using ratio of rise : run

You can easily convert this ratio in an angle in degrees using trigonometry.

Roof Pitch Calculator

The above Roof Pitch Calculator is a simple and easy to use online tool that allows you to calculate the pitch of a roof using various inputs. Here is how you can use this roof slope calculator:

At the top, you can see a form with a drop-down menu labeled “Select Input Type”.

In the drop-down menu, select the type of input you want to provide. The options are “Rise & Run”, “Rafter Length & Rise”, and “Rafter Length & Run”.

Based on your selection, the appropriate input fields will be displayed. For example, if you select “Rise & Run”, the input fields for “Run” and “Rise” will be displayed. If you select “Rafter Length & Rise”, the input fields for “Rafter Length” and “Rise” will be displayed.

Enter the appropriate values in the input fields. For example, if you selected “Rise & Run”, enter the rise and run measurements in feet in the corresponding input fields.

Click the “Calculate” button. If the input fields are not filled out correctly, the calculator will show you the results in the separate field below the form.


So, you see understanding the pitch of your roof is crucial for a variety of home projects. There are multiple ways to calculate the pitch, so find the method that works best for you. With the right tools and measurements, you’ll be able to figure out the pitch of your roof with ease.

David Noah

Howdy, I’m Noah Although I don't like all this internet thing but I love sharing my stories on the roof here. With my years of experience in number of roofing contractors across various boroughs of Florida, I'm here to answer all your roofing questions. I'm really honored to have you on my website browsing through our articles and hope you'll enjoy your visit and find my content helpful in every situation. You can contact me right away to discuss any of your roofing problem.

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