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How to Determine Roof Pitch

How to Determine Roof Pitch

If you are completely clueless about how to determine roof pitch of your house, this article will be an insightful read. Here I provide you with easy to follow guidelines on figuring out the exact roof pitch dimensions.
Omkar Phatak
The fact that you are looking for guidelines on roof pitch calculation means that you are probably thinking of putting up a new roof. Either that or you are building a new house from ground up and need to decide on the right roof pitching. In any case, this DecorDezine article explaining the calculation of roof pitch will be a helpful read. If you are already aware of the calculation procedure for roof pitch measurement, you can enter the rise and run values in inches, in the online roof pitch calculator presented below, to get the pitch value, along with the angle.

Roof Pitch Calculator
Enter Roof Rise Value in Inches
Enter Roof Run/Span Value in Inches
Roof Pitch Value =
Roof Pitch Angle = Degrees

Traditionally, house roofs tend to be pitched or angled to prevent snow and water from accumulating up there. Depending on roof styling and architectural design, the roof pitch value may vary of course. For putting up a new roof, you need to size up the dimensions of the existing roof and therefore, determining the pitch is an essential part of the job. Let me define roof pitch, before elucidating its calculation.

What is Roof Pitch?
For those of you who are confused about what is meant by a roof pitch, here's a simple explanation. It's a measure of the steepness of a roof. In mathematical language, the roof pitch measurement is similar to calculation of slope for a line in a plane. The roof pitch is a ratio of 'rise' of the roof (vertical height) to its span or run (the horizontal expanse). Generally, the roof pitch is defined as rise of the roof for every 12 inch increase in horizontal expanse. If you consider the triangle formed by the gable of the roof, the roof pitch is the tangent of the base angle. So if you know the roof pitch value, which is a ratio of the hypotenuse of the gable triangle with its base, you can take the tangent inverse of it, to get the roof pitch angle.

How to Calculate Roof Pitch?
To be able to measure the roof pitch, you will need a carpenter's level and a measurement tape or scale. Using a ladder, position yourself in such a way that one side of the roof slope faces you. Mark 12 inches in length from one end on the level, using a pencil marker. Place the level horizontally with one end touching the roof.

Once you are sure that the level is perfectly horizontal, measure the perpendicular distance in inches, from the 12 inch mark on the level, to the roof, as shown in the accompanying illustration, using a measurement scale or tape. Divide that measurement (known as the rise of pitch) by 12 inches (which is the default span or run value) to get the roof pitch value. For example, if the measure value is 4 inches, the roof pitch will be 4/12 = 1/3 = 0.333.

How to Determine Roof Pitch Angle
To determine the roof slope angle from the roof pitch, take the tangent inverse of that value using a scientific calculator. For example, in the above example, since the roof pitch value is 0.333, the roof pitch angle is tan-1 (0.333) = 18.435°. If you have the rise and run value, you can use the calculator provided above to directly get the roof slope angle value.

Be careful when using the ladder to make roof measurements. Have somebody help you out and let him hold the ladder while you are measuring the roof pitch. As explained before, all you have to do is measure the 'rise to run' ratio to determine the roof pitch value. The higher the pitch value, steeper is the roof and greater is the pitch angle. Using the roof pitch calculator provided above, you can easily measure the value and know the pitch angle.