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How to determine roof pitch?

Oct 6

The pitch of a roof's angle is the roof's vertical rise for every 12 horizontally. A roof with a pitch of 6 inches per 12 inches horizontally will have a pitch of 6-in-12.

How to Measure Roof Pitch

Knowing the pitch of your roof when adding skylights or designing an addition is essential. This is a safe and easy way to find the pitch of your roof from within your attic.

  1. You will need a tape measure, an 18- to 24-inch level, and a pencil to measure the pitch of your roof.
  2. Measure 12 inches from the end of your level, and mark it.
  3. Next, position the end of your level in the attic against the roof rafter's bottom and ensure it is perfectly level.
  4. Measure vertically, starting at the 12-inch mark at the level and going up to the underside. This measurement indicates the height of the roof is 12 inches.

How To Calculate Roof Pitch in Degrees

There are several ways you can measure the pitch of your roof. A measuring tape, spirit level, and calculator are all you need. These tools will allow you to access your loft space and help you remember the maths you learned in school.

  1. Measure the length of your roof. This is the horizontal distance between your roof's peak and the wall. This can be done with a spirit level or tape measure.
  2. Next, calculate the rise. This is the height of the structure wall above your apex.
  3. Divide the rise by run. This will give the roof's tangent. (rise / run = tangent)
  4. Divide 1 by your Tangent.
  5. Then multiply this number by 180/p to get your roof pitch.

REMEMBER: Roof pitch = (1 / Tangent, Rise / Run)*180/p


 Rise at 8m and Run at 5m.

  1. 8 / 5 = 1.6
  2. 1 / 1.6 = 0.625
  3. 35.80986 - 0.625 x 180/p = 0.525
  4. The roof pitch is, therefore 35.81deg

Calculating Roof Pitch in a Ratio

It is traditional to measure roof pitch by displaying it in a ratio of X to 12. This is accomplished by measuring how high a roof rises vertically relative to its horizontal extension. It's easy to do and will require the same tools.

  1. Place one end of your spirit level against the roof deck. Measure to determine the point 12 inches along your level. This is the run.
  2. Now, place your tape measure vertically against the run line and measure the distance between your spirit level at the mark and roof deck. This is your rise.
  3. You will need to calculate your X:12 ratio based upon rising.
  4. You can convert this ratio into an angle.

Using a Roof Pitch Calculator

There are many options online and in smartphone apps to help you calculate your pitch. This is a more straightforward option than using pencils and paper. These calculators require the same rise and run measurements you need to calculate manually. Some more advanced calculators can show you your roof pitch by taking a picture. 

However, these calculators have their limitations. Photo-based calculators can be inaccurate if the lighting conditions or camera angle aren't perfect. You might also need to know how many numbers you will need before the calculator can calculate your pitch. These apps and tools are improving all the time. They offer homeowners an alternative that can help them access their roof space.

A Pitched Roof is Important

A roof that doesn't have any pitch is a roof that's at high risk of collecting standing water. This can lead to roof damage and the inevitable possibility of water leaking into the building. Flat roofs may have a slight pitch to allow water run-off from rain or snow.

In areas where snow can accumulate, pitched roofs are more critical. The roof's pitch is more important than the amount of snow it can hold. This accumulation could cause damage to the roof's interior structure. A higher pitch roof can handle heavy rain and snow, which can help to remove any structural problems.

The following can have an impact on a home's roof pitch:

  • Attic Space: A higher roof pitch creates more storage space in an attic.
  • Construction Materials: A roof's pitch determines how many materials are needed to cover it.
  • Energy Efficiency Pitched roofs are an energy-efficient home environment that provides natural ventilation and reduces energy loss.
  • Resilience to Wind: Research suggests a ">exceed 45 degrees angle or pitch ratio greater than 12:12.


Now you should better understand how to calculate the pitch for your roof. There are many methods to calculate your roof pitch. You have to choose the one that works best for you. It is possible to determine the pitch of your roof, whether you are looking at replacing tiles or considering extensions.