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How to Calculate Roof Pitch?

Before mastering the techniques on How to calculate roof pitch, it is necessary to differentiate between roof pitch and roof slope because both terms are often used interchangeably. The pitch of a roof brings convolution to the measurements and this complexity is paramount to the best architectural design of your properties.

The angle at which the roof rises from the lowest point to the highest point is called the pitch of the roof, or simply, roof pitch. It is measured as a ratio and the numbers are separated by placing a colon mark or a slash mark.

For instance, if the measurement of a roof pitch is calculated to be 4:12 or 4/12, it refers to a rise of 4 inches for every 12 inches of the roof run. Therefore, in this example, the first number (4) is referred to as roof rise, whereas the second number (12) is called roof run.

What’s the Difference Between Roof Pitch and Roof Slope?

Owing to the complexity of how to calculate roof pitch and the regular usage of the terms such as roof pitch in practicality, almost all roofers consider the pitch and slope as the same thing.

The slope of a roof is measured as the rise over run, while pitch refers to the rise over the span. Span is the entire horizontal measurement of the roof; therefore, it is equal to twice the run. Technically, what you’ll see referred to as pitch is the slope of the roof in reality. That’s why the terms seem to interlink with each other as if they’re cut from the same cloth.

Types of Roofs


Now you are aware of the fact that the traditional way to express roof pitch is demonstrated as a ratio between rise and run, written as x:12, where ‘x’ is variable. In the case of 1:12, the rise is equivalent to one yard for every twelve yards of building length. The design of roofing can be categorized according to the roof pitch calculations:

Also Read: Types of Roof Installation

1. Flat Roofs

In reality, flat roofs aren’t perfectly flat at all. The maintenance of the merest slope is constructed to prevent the accumulation of water or to promote water runoff. You may muddle about how to calculate the roof slope for such a piece of construction. A general rule of thumb is to calculate it as ½:12 or 2:12.

2. Low-Pitched Roofs

The pitch of these roofs is lower than the usual designs but higher than flat ones, that is, 4:12. To avoid the probability of leaks, specialized materials are required to maintain their repair and restoration.

3. Conventional Roofs

Conventional roofing designs are the easiest to build and the safest to walk or work on. Their pitch ranges from 4:12 to 9:12.

4. High-Pitched Roofs


As the name indicates, high-pitched roofing designs should be maintained using additional fasteners and their slope may reach up to 21:12.

How to Calculate Roof Pitch for Accurate Measurements?

The concept behind how to calculate roof pitch is based on the theory of a right angle triangle. In simple words, a triangle is said to be right-angled if one of the three angles is perpendicular which means to be equivalent to 90 degrees, denoted as 90°, and the sum of the remaining two angles makes 90°. To further ease the notion for you, roof pitch defines the slope created by the rafter.

Call any of your mathematician friends and get his/her help because the following equations are used as a foundation to calculate roof pitch. It is advised to use a scientific calculator to make these estimates.

  • Pythagorean Theorem: a2 + b2 = c2; where rafter2 = rise2 + run2
  • Pitch = rise/run; where pitch is expressed as a percentage (%)
  • Pitch = tangent (angle) = tan θ; where the angle is the roof pitch expressed in degrees.

In the case of estimating the slope of the pitch in the form of x:12, measure the slope and substitute 12 with the run length. The answer or value of x will denote the roof rise.

Is there a Standard Pitch of a Roof?

There is no universal or standard for any roof because the value entirely depends on the geographic location, climatic conditions, culture and styles of the houses in your area of residence.

How to Calculate Roof Pitch in Degrees?

All you need is a measuring tape, a spirit level, a scientific calculator, and above all, a sound mind to measure the pitch or slope of your residential or commercial buildings.

  • Measure the distance between the peak of your roof and the wall where it ends. This length or distance is referred to as the run of the roof and can be assessed with the help of a measuring tape or a spirit level.
  • Now measure the distance between the height of the roof's apex above the structured wall, which is called the rise of the roof.
  • Divide the value of rise by the value of run. The resultant will be the tangent, or tan, of the roof. (rise / run = tangent).
  • Use the arctan function on your calculating device (tan-1) and you’ll obtain an answer which should be multiplied by 180/π to get the exact measurement of your roof pitch.


Now that you’ve gone through the entire procedure of how to calculate roof pitch, you just need to figure out the method with which you’re best familiarized. Measuring the roof slope is helpful in ways ranging from repairing the roofs, replacing the tiles and the feasibility of extensions. Read out the article again and don’t hesitate to reach out for help.

Read More: Average Cost of Roof Replacement