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How To Calculate Roof Slope

Table Of Tangent Values For Each Angle In Degrees

How to Calculate Roof Pitch

Just type “tangent table” into your search engine and you’ll find a table something like the one we show below.

To convert a slope into rise/run is to use the tangent of that slope or angle

That number, a constant, lets us calculate rise if given run or run if given the rise amount.

Definition of Tangent: the Tangent of any angle is defined as the vertical rise divided by the horizontal run.

A tangent is also defined as a ratio of two lengths: the length of the side of the triangle opposite the angle divided by the length of the adjacent side of the angle.

For a right triangle in which the roof rise is the vertical line opposite the roof angle or slope, the tangent of the roof angle is the ratio of roof rise over the length of the sloped roof surface.

In the illustration at the start of this article, the tangent T of the 38 degree angle is the ratio:

Roof Rise / Sloped Roof Run

So we write the tangent of angle A as:

Tan < A = Rise / Run

Our sketch above shows how we calculate the rise per horizontal foot of run when we are given the roof slope in degrees .The purple sloped line is the sloping roof surface or the slope or angle of a stairway.

Standard rise & run: Roof slope or stairway slope are properly expressed of inches of vertical rise per foot or 12-inches of horizontal run or distance traveled.

Luckily, using the Tangent function, and given the angle of any stair or roof, we can calculate the amount of rise for any horizontal distance.

Tan 38o = 0.7813

Tan 45o = 1.00

The Importance Of Roof Pitch Angles

You may be wondering why its so important to calculate your roof pitch angles. Well, a lot of it has to do with the quality of your home and its resale value.

Its also possible that you could save money on utility bills if you have a more efficient roof, which is all influenced by pitch angles!

It is much harder to install a new roof on a home that has a low pitch, but with the proper equipment and time you may be able to accomplish it.

In addition, if your roof is too steep for you, then theres no way that youll be able to do it without professional help!

Jumping into installing a new roof without calculating the roof pitch angle first can end up causing more headache and money.

If youre worried about making mistakes and doing it wrong, then hire a roofing contractor to do the work for you.

Hopefully, weve helped you learn some basics about your roof pitch angles and how to calculate what kind of slope or rise that you have!

This will be an important step in applying any roofing or shingles that you house.

Having a good understanding of what your roof pitch is will help you maintain your home and make it more efficient.

It can also help to add value to the property if you ever consider selling if you are in the buy and well business.

The Importance Of A Pitched Roof

If a home orbuildingâs roof didnât have any pitch at all, it would be at a high risk ofcollecting standing water that ends up deteriorating the roof itself,presenting a serious and inevitable risk of leaking through the roof and intothe building. Even on roofs that may appear flat to the naked eye, a slightpitch has probably been built into the roof to facilitate water run-off fromrain and snow.

Pitched roofsare even more important in regions where snow can accumulate on a roof. Thelower the pitch, the greater the amount of snow that can accumulate on theroofâs surfaceand the weight of this accumulation could potentially break theinterior structure of the roof itself. With a higher roof pitch, snow and heavyrainfall can be sloughed off before structural integrity becomes a concern.

Roof pitch canalso have the following implications on a home:

Also Check: Metal Roof Skylight

Read Also: How Do I Know If My Roof Is Leaking

Shed Roof Pitch Calculator

Knowing how to calculate roof pitch, rise, run, and ridge board height is essential to any shed construction. A roof pitch calculator can make things much easier. Simply plug in the values of your roof and it will show you slope percentage, degree, and even length.

Even seasoned DIYers use this tool to check their measurements against their own, and I would advise having this tool nearby the next time you build a shed roof.

Determine The Roof Slope Multiplier

Roof Pitch Formula

Note: If you already know the roof slope in degrees, then all you have to do to find the roof slope multiplier is find the secant using a scientific calculator.

For example, if the roof slope angle is 45°, then sec = 1.414213. That will be your roof slope multiplier.

So, to proceed.

Once you have the slope of the roof expressed in standard pitch, you can consider yourself in possession of the lengths of the a and b sides of a right triangle. Now you need to pull out your trusty Pythagorean Theorem and figure out the length of the hypotenuse.

A good calculator can be found at web2.0calc.com.

As Im sure you remember, a² + b² = c². So, if your slope is 6:12,

6² + 12² = c²

36 + 144 = c²

13.416 = c

So 13.416 is the length of the hypotenuse.

Now that you have the length of your hypotenuse, 13.416, you want to think of that as the length of a line on the actual sloped roof surface over a horizontal distance of 12 inches. You want to find out how much longer that line is than the 12 inches it covers.

You will express this difference as a number, called the roof slope factor .

Once you know the roof slope multiplier for any particular roof slope, you can use it to find the actual area of a roof of any size that has the same slope.

So in this case, for every 12 inches the roof goes across horizontally , while rising 6 inches , theres actually 13.416 inches of roof .

If you divide the 13.416 inches by the 12 inches , that gives you 1.118.

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Roof Pitch Calculator Use :

Steps to use this calculator are mentioned below:

  • This online calculator is very user-friendly.
  • To begin, determine the length of your roofs run. This is the distance between the apex of your roof and the wall in the horizontal plane. You can use a tape measure or a spirit level to do this.
  • The next step is to measure the rise. This is the distance between your apex and the structures wall.
  • Enter the details in the above calculator and the results will be displayed.

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Gable Roof Sheathing Calculator

Estimate the amount of plywood or OSB needed for sheathing a roof.The calculation is based on that the Plywood or OSB sheets are of a 4Ⲡx 8Ⲡsize. One sheet = 32 ft²

This basically calculates the number of sheets needed for a Gable roof.The square footage of a Hip roof area is identical to the square footage of a Gable roof of the same measurements. If you are calculating the number of sheets needed for a Hip roof then for the value of the gable overhang use the eaves overhang dimension, assuming it is the same all around.The amount of waste on a Hip roof will be higher than for sheathing a Gable roof and even more so if you are using OSB sheathing. OSB sheathing has a rough side and a smooth side. You always want to make sure the rough side is up with OSB sheathing. Never install the OSB sheathing with the smooth slippery side up!

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Four: Measure With A Speed Square

How to Determine the Pitch of a Roof

You can also use a speed square and level to quickly measure the roofs pitch. Set the level on the edge of the speed square as shown below, then place the heel of the speed square on a rafter or gable edge of the roof.

Holding the level and speed square level, locate the measurement on the speed square where it meets the rafters bottom edge to find the angle of the roof in degrees.

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How To Calculate Roof Pitch As A Ratio

The traditional method of measuring roof pitch is to display it as a ratio of X:12. This is done by measuring the number of inches a roof rises vertically for every 12 inches it extends horizontally. This is simple to do, and youll need the same tools and access to your roof space as above.

  • First, place one end of your spirit level against your roof deck. Then measure to find and mark the point 12 along your level. This is the run.
  • Now, rest your tape measure vertically against your run line, and measure the distance between the top of your spirit level at the mark and the roof deck. This is your rise.
  • Now you should have your X : 12 ratio based on rise : run.
  • If youd like to convert this ratio to an angle you can do so.
  • How Is Roof Pitch Calculated With Rise And Run

    It is a simple calculation using the formula:

    $$Pitch = $$

    Youre probably wondering:

    How can we compute the RAFTER LENGTH, GRADE, and ANGLE?

    Once you know the rise and run, equations for a right triangle can be used to determine the rafter length, roof angle, and grade.


    This is the famous Pythagorean Theorem!

    $$\text = $$

    and so

    $$Angle = arctan$$

    The grade is the pitch expressed as a percentage:

    $$Grade = \Bigr100$$

    And not only that:

    The roof slope calculator also works if you only know the RISE and RAFTER , or if you know the RUN and RAFTER .

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    Technical Reviewers & References

    Slate Roof In Australia

    Roof pitch calculator

    One of the most popular types of roof that is used in Australia is the slates. The slates are made to be attached to the other materials that are used for the roof. These are mostly found in Australia because they can work well with the climate and environment.

    Additionally, slate roofs are most often found in regions that receive heavy snowfall like Scandinavia and Northern Europe. The steep slopes prevent the weight of the entire roof from adding to the pressure on the joints which can lead to damage or leaks after there is a large amount of snow that has fallen on it.

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    How To Calculate Roof Pitch In Degrees

    There are a few ways to measure or work out the pitch of your roof. All youll need to hand will be a measuring tape, spirit level and calculator. With these tools in hand you just need access to your loft space and to remember some of the maths you learned at school.

  • First, you need to measure the run of your roof. This is the horizontal length that spans between the peak of your roof and the wall. You can do this with a tape measure or spirit level.
  • Next, you need to figure out the rise. This is the height of your apex above the structure wall.
  • Now, divide the rise by the run. This will give you the tangent of the roof.
  • Then, divide 1 by your tangent.
  • Finally, multiply this result by 180/ and you’ve calculated your roof pitch!
  • REMEMBER: Roof Pitch = )*180/

    Example: Rise of 8m and Run of 5m.

  • 8 ÷ 5 = 1.6
  • Therefore, the roof pitch is 35.81°!
  • How To Calculate The Roof Pitch

    How to calculate the roof pitch | pitch formula for roof | how to determine the roof pitch | how to calculate pitch on roof | how to calculate pitch of a roof | how to determine pitch of roof.

    Everybody need a new house with a classical appearance, roof is the one of the most important part of any building structure that prevents the the other structure of building and inhabitant from adverse climatic weather condition and also ensure the privacy for the inhabitants. In earlier time from the beginning of civilization peoples are always looking for or house which built by timber covered with roof to prevent from heavy rainfall and snowfall conditions.

    Design and construction of roof is depending on many factors but one of the most common important factor is climatic and weather condition of your surrounding areas, in your cities and countries. The area which has heavy rainfall and snowfall require good drainage for roof, roof drainage depending on slope of the roof provided, based on slope of roof it is categorised into two types flat roof and pitched roof or sloping roof. These are two types of roof structure based on slop.

    One may ask, how to calculate the roof pitch?, to determine the roof pitch or pitch of roof you need Pitch formula for roof calculator, by means you can easily calculate value of roof pitch in fraction, in ratio and angles in degrees, you can also calculate length of rafter, rise height per foot run, roof height and span.

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    How To Work Out Your Roof Pitch

    Unless you work in construction or youve worked on a roof before, its unlikely youll know how to calculate your roofs pitch. This information is incredibly useful for a range of home projects, but absolutely vital if your next DIY endeavour involves your roof. This applies whether youre completely replacing the roof covering or installing a brand new roof window. To do these jobs correctly, you will need to be able to figure out the pitch of your roof.

    How To Determine The Roof Pitch

    How to find Roof pitch or slope

    take the measurement of horizontal run length:- it is horizontal distance out side of walls top plate to a point directly below the centre of the Ridge or hip of roof, assuming it is 4 meters

    measure the vertical height of rise of your roof, assuming it is 1 meters.

    to calculate pitch of a roof as the proportion of rise and run as pitch = rise/ run, pitch = 1/4 = 1/4, which is equal as 25%, hence pitch for roof will be 25%.

    Recalculate the value of pitch in angle in degrees, as pitch = tan , so angle = arctan = arctan = 14°, hence pitch for roof will be 14 degrees.

    to calculate pitch on roof is in the form of X:12, as pitch = X/12, so X = pitch × 12 = 0.25 ×12 = 3, hence pitch of your roof will be 3:12, and it can be also express in fraction as 3/12, or 3 in 12, or in percentage as 25%.

    Read Also: How To Add A Gable Overhang

    How To Measure Roof Pitch

    Knowing the pitch of your roof is useful when designing an addition, installing skylights, or cutting new rake boards. Here’s an easy, safe way to determine the pitch from inside your attic.

  • To measure the roof pitch, you’ll need an 18- or 24-inch level, a tape measure, and a pencil.
  • First, measure 12 inches from one end of the level and make a mark.
  • Then, in the attic, place the end of the level against the bottom of a roof rafter and hold it perfectly level.
  • Now measure vertically from the 12-inch mark on the level straight up to the underside of the rafter, as illustrated. That measurement is the number of inches the roof rises in 12 inches.
  • 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.

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    How To Use The Roof Pitch Calculator

    This roof pitch calculator or roof slope calculator is a simple, easy to understand tool to use when you need to perform construction work in your home. To use this, you must take the required measurements so you can input them in the required fields. Here are the steps to follow for the roof angle calculator:

    • First, enter the value of the Rise and choose the unit of measurement from the drop-down menu.
    • Then enter the value of the Run and choose the unit of measurement from the drop-down menu.
    • Finally, enter the value of the Rafter Length and choose the unit of measurement from the drop-down menu.
    • After entering all of the values, the roof pitch calculator automatically gives you the values of the Roof Pitch, Roof Pitch , and Roof Pitch .


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