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How To Measure A Triangle Roof

What Is The Standard Pitch Of A Roof

“A Roof Over Your Shed” (part1)… Using Similar Triangles

Roof pitch refers to the measurement of the slope of a roof and you express this as a ratio. Although theres isnt any standard pitch of a roof used on all kinds of sloped roofs, you can determine the range of pitches by using a roof angle calculator and by considering factors like the local climate and roofing materials.

Express roof pitch as the ratio of the amount of the vertical rise of a roof or rise over the corresponding horizontal distance or run. You write the pitch assuming a run of 12-inches thus, the ratio would describe how much a roof rises for each foot of the run.

As aforementioned, there is no standard pitch of a roof. But the most commonly used pitches range between 4/12 and 9/12.

Roof Pitch To Angle In Degrees

Roof pitch formula help you to convert roof of pitch ratio or fraction of slope in angle in degrees in following two steps:- 1) divide the first part of the ratio by 12 to figure out the pitch and 2) find the inverse tangent of pitch to find the angle in degrees.

For 2/12 roof pitch into angle in degrees:- 1) pitch = rise/run such as 2/12 = 0.1666, 2) tan inverse of pitch = tan-1 = 9.46°, thus a roof pitch of fraction 2/12, or 2 in 12 slope, or in ratio 2:12 is equivalent to 9.46 degrees.

For 4/12 roof pitch into degrees:- 1) pitch = rise/run such as 4/12 = 0.33, 2) tan inverse of pitch = tan-1 = 18.43°, thus a roof pitch of fraction 4/12, or 4 in 12 slope, or in ratio 4:12 is equivalent to 18.43 degrees.

For 7/12 roof pitch into degrees:- 1) pitch = rise/run such as 7/12 = 0.583, 2) tan inverse of pitch = tan-1 = 30.26°, thus a roof pitch of fraction 7/12, or 7 in 12 slope, or in ratio 7:12 is equivalent to 30.26 degrees.

Measure Slope Using A Speed Square

Using a tool like speed square can expedite the calculation. You can quickly measure the roof pitch by setting the level on the edge of the speed square.

Holding it and checking the point where it meets the rafter edge will get the roof slopes angle on the speed square in degrees. You can convert degrees into a standard 12-inch fraction.

Read Also: Extending Roof Overhang

S To Convert Roof Pitch From Inches Per Foot To Angle In Degrees

Sometimes, you may need to convert the roof slope in angle form. Here you will use the slope inverse tangent formula. First, make the slope rise and run the figure into a fraction. E.g., the rise of 4 and run of 12 means the slope in a fraction is 4/12. Now divide it to get the decimal value of 0.33. Now the angle is ArcTan or 18.42 degrees

Determine Roof Pitch And Slope Factor


The pitch of your roof can dramatically increase its surface area, so its important to take it into account in your estimation. Simply use a 12-inch level to measure how many inches it rises for per foot it runs. This can help you determine your roofs slope factor. You can use pre-made tables online, or you can calculate it yourself. Simply square the rise and run of your roofs slope, add them together, then find their square root and divide it by 12.

In this case, lets assume your roof has a pitch of 3/12, which means for every twelve inches of length, it will rise by two. Your roofs slope factor would then be equal to ) / 12 in, or 1.03078. Most tables will round this to 1.03.

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Draw Each Shape Individually Calculate Each Area And The Total Square Footage Of Your Roof

Now we have eight shapes to find the area of six triangles and two rectangles. Instead of breaking out the old textbooks to calculate triangle areas, we like to use a triangle calculator. It makes figuring out the area of triangles a lot simpler.

In the example above, we have two triangles with sides of 30, 20, and 20 feet. Pop those figures in the three-sides calculator and youll get an area of 198. Since we have two of those triangles, multiply by 2 for a running total of 396 square feet.

We have four remaining triangles, all with dimensions of 15, 20, and 25 feet. That same calculator reveals a result of 150 square feet. Since there are four of those triangles, multiply by 4 to get 600 square feet.

Lastly, we have two rectangles of 15 by 30 feet. This one is easy, just width times height for a total of 450 square feet for each one. Multiply by 2 and their total square footage is 900.

Adding all the areas up yields a total of 1896 square feet . Since roofing material comes in 100 square foot squares, youll need at least 19 of them for your roofing project. Itd be wise to get at least 20 to account for mistakes and waste.

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The Type Of Roof You Want

The type of roof you want will have a big impact on the cost of your roof replacement. There are a variety of different types of roofs for you to choose from based on your budget and the look you want.

If youre on a tight budget and looking for an affordable roof, an asphalt shingle roof might be right for you. But if youre looking to upgrade to a longer-lasting and sharp looking roof, theres the standing seam metal roof.

Asphalt and metal are two of the most commonly seen roof types, but there are also premium shingle roofs that come at a premium price. These roofs give you a unique look that really stands out. These premium roofs include cedar shake, slate, and tile.

The premium shingle roofs can get expensive quickly and be more than triple the cost of an asphalt shingle roof.

The Operating Cost Of Your Roofing Contractor

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Every roofing contractor has operating expenses to keep their business going. These operating costs will always factor into the price of any roof work that needs to be done.

Some common operating costs are:

  • Building cost and utilities, shop and truck yard
  • Advertising and promotions
  • Payroll and payroll taxes
  • Taxes

These are just some of the fixed operating costs that it takes to run a business. No matter if a roofing company does a simple repair or replaces 10 roofs, these are the costs that have to be paid every day. No matter what work you get done or what service you need, operating expenses will always factor into an estimate or final cost.

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What Is A 4/12 Roof Pitch

A 4/12 is a roof slope that rises by 4 inches for every 12 inches across. This forms an angle of 18.5° between the horizontal section and the roof, and creates a gentle incline that is seen as a midpoint between a low-pitch and medium-pitch roof. A 4/12 slope is enough to accommodate water runoff, but is not suitable for regions that are affected by heavy snowfall. Standard asphalt and composition shingles are the best for a 4/12 roof rubber and wood shingles are unsuitable.

Roof Area Calculationsmethods For Calculating The Area Of A Roof Depending On What Measurements You Already Know

  • about types of roofing materials, installation, inspection, diagnosis, repair, maintenance, & warranties

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Roof area calculation & measurement methods:

Here we describe various methods for measuring all roof data: roof slope or pitch, rise, run, area, and other features. We include on-roof measurements, roof measurements or estimates that can be made from ground level, and several neat tricks using a folding ruler to measure roof angle or slope.

This article shows how simple measurements can give the roof area without having to walk on the roof surface. This article series gives clear examples just about every possible way to figure out any or all roof dimensions and measurements expressing the roof area, width, length, slope, rise, run, and unit rise in inches per foot.

We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

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How To Measure Or Estimate The Total Roof Area

If you have safe access to the roof surface you can quickly make the needed area measurements: just measure from the ridge to the lower edge or eaves, keeping your tape straight.

With a decent 3/4″ or 1″ wide 30 ft. tape measure you can extend the tape out to catch the roof eaves without having to walk dangerously close to the roof edge. Also measure the roof edge or length.

  • RW = Roof Width = dimension from ridge to eaves. In my sketch I use or the dimension of the sloping surface as RW. Remember to include in the amount by which the roof extends out over the building walls – its eaves.
  • RL = Roof Length = dimension of the roof from one gable end of the building to the other. You don’t see RL in my sketch at left. RL is simply the building width plus the amount of overhang at the two gable ends of the building.
  • RA = Roof Area = RW x RL
  • Well this is only true provided the roof surface is a rectangle. If you are working with hips and gables and you want to get precise area measurements you may find it easiest to divide the individual roof slopes up into sub-components: a rectangular part and a triangular part.
  • For a rectangle just multiply the width and length of its two sides to obtain area.
  • For a right triangle, its Area = 1/2 x
  • For a triangle such as the red example in our photo, just divide the triangle into two halves and you can still make these calculations with ease.
  • Remember to keep your dimensions all the same .
    • Roofing Squares = RA / 100

    How To Calculate Roof Area

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    Before you begin work on any roofing project, its vital to have an accurate measurement of your roof area. This will allow you to work out everything from how many roof tiles you need to project cost and timeframe for completion. Thankfully, calculating your roof area is a quick and easy process once you know how. In fact, for the classic gable roof that most British homes have, you can work out the size of your roof with just two measurements.

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    One: Get Up On Your Roof Safely And Take Initial Measurements

    Sketch out the shape of your roof on graph paper. In this example, youd only need to measure overall width and length, the central ridge, and one of the hips . If you have a more complex roof shape with dormers, take all the measurements you can and prepare to use your eraser to refine the image of your overall roof structure. Make sure you have solid footing and if possible, use fall protection to keep yourself safe. Be mindful of hazards like ridge vents. Note the lengths in feet:

    How Various Roof Measurements Are Calculated

    Details for calculating roof area are at ROOF AREA CALCULATIONS

    RA = Roof Area = RW x RL

    If you have safe access to the roof surface you can quickly make the needed area measurements: just measure from the ridge to the lower edge or eaves, keeping your tape straight. With a decent 3/4″ or 1″ wide 30 ft. tape measure you can extend the tape out to catch the roof eaves without having to walk dangerously close to the roof edge. Also measure the roof edge or length.

    • RW = Roof Width – dimension a in my sketch at left. Remember to include in the amount by which the roof extends out over the building walls – its eaves.
    • RL = Roof Length = dimension of the roof from one gable end of the building to the other. RL is simply the building width plus the amount of overhang at the two gable ends of the building.

    Details for calculating the slope, pitch or grade of a roof or any other surface are


    Slope is simply the relationship between increase in height and horizontal distance traveled. In my sketch above if we travel up my triangle along from left to right, we will cross a horizontal distance and we will ascend in height an amount .

    Slope or pitch or grade has several means of expression: Rise/Run, Angle in degrees, Tangent, Pitch, or Percent Grade – all compared in our little table below.

    Tangent = Rise / Run

    E.g. Tan = 1.00 – that is, we will travel 12″ up for 12″ of run

    Below is a tiny summary that shows the range of these values.

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    Calculate Roof Pitch From The Ground In Three Quick Steps

    Roof pitch is one of those things that middle school math and geometry instructors can easily point to, and say, See? Learning how to work with rise over run is fun and useful, right? If at any moment you start having PTSD flashbacks to algebra or geometry class, take a deep breath. Well walk you through this slowly in three simple steps. All you need is a tape measure, and possibly a helper to hold it.

    Step One: Grab that tape measure, notepad, and pencil and head outside. Find the slope of your roof youd like to measure, and start measuring the distance from the outer edge of the eave to the point at which the plane of the roof slope is barely visible to your eye. Write that number down in both inches. This figure is the horizontal run.

    Step Two: Stand directly underneath the gutter or edge of the roof plane you want to calculate the slope for. Measure the distance from your eye to the top of the drip edge of your roof overhang. Write that number down in inches, too. This figure is the roof rise.

    Step Three: Take the roof rise figure in Step Two and divide it by the horizontal run from Step One. In the example above, the rise is 60 inches and the run is 120 inches. This reduces down to a roof pitch of 6/12. Well use this figure in just a bit, so keep it handy.

    Measure Roof Slope From The Ground Using A Folding Carpenter’s Rule

    How To Measure Roof Slope From The Attic, Rooftop, And Gable

    As you’ve see from out other roof measurement examples beginningat ROOF MEASUREMENTS, knowing the roof slope is really handy as something we can measure up close but also from a distance, obtaining a number that plugs into simple formulas for roof area too.

    What if the roof is inaccessible from outdoors, and there is no access to the building interior so we cannot make direct roof slope measurements, but we still need to know its slope?

    You need a simple folding carpenter’s rule. It helps to have a steady hand and to read the instructions on exactly where to read the inches on the bottom scale in the folding rule triangle that we show at left.

    Details of how to use a folding carpenter’s rule to obtain roof slope, area, and other measurements along with a table that translates inches along the bottom scale of the folded rule into roof slopes areat ROOF MEASURE by FOLDING RULE

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    How Do You Calculate The Square Footage Of Your Roof

    Is it time for a roof replacement? Are you trying to figure out how much youll have to invest in your new roof?

    If so, youre probably overwhelmed trying to learn everything that goes into the cost of your roof replacement. To help you understand the size of your roof investment, you first need to know the size of your roof. Thats why were going to break down how to measure your roofs square footage.

    The team at Bill Ragan Roofing has been repairing and replacing roofs in Nashville and surrounding areas since 1990. We take extreme pride in everything we do, especially our workmanship.

    Other Complex Roof Examples

    Any roof can be simply divided into squares, rectangles, triangles, and trapezoids. If this is not initially clear, just sketch the shape of your roof on a sheet of paper.

    Start by sketching all the squares and rectangles, and then look for all the triangles. In this way, even if you have a hip-shaped roof on one part of your home and a gable-shaped roof on the other side of your home, you can still come up with an approximation of the overall roof.

    For example, a hip roof consists of 4 different geometric planes, 2 of which are trapezoids and 2 of which are triangles. Just calculate each figure, and then add them all up.

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