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HomeExclusiveHow To Measure A Roof In Square Feet

How To Measure A Roof In Square Feet

How Many Extra Shingles Should You Buy

How to Measure the Square Footage of a Roof

If you order shingles based solely on the area of the roof, you wont have enough. Youll need shingles for starter courses along the eaves and sometimes at rakes, and youll need shingles to cap hips and ridges. Cutting shingles also generates waste. In some places, including at the rakes, against walls and chimneys, and at valleys, youll need to cut shingles. Some of the cutoffs will be big enough to use as starter shingles or in other areas where cut shingles are needed, but smaller cutoffs will be waste.

Calculate The Exact Roof Area

Follow these steps to figure out the exact area of your roof:

  • Take your pitch number and divide it by 12. For example, if your pitch is 4 in 12, you need to divide 4 by 12. The answer will be 1/3.
  • Next, you need to square your outcome. In our example, 1/3 squared will yield 1/9.
  • Thereafter, add 1 to your result: 1/9+1=10/9
  • Calculate the square root of your new number: The square root of 10/9 is 1.05.
  • Measure the length of your house including the overhangs.
  • Measure the width of your house including the overhangs.
  • Multiply the length of your house by its width to get the area. For example, 40 feet x 20 feet = 1,200 square feet.
  • Thereafter, multiply the area by the pitch to get the true roof area: 1,200 x 1.05 = 1,260 square feet.

In order to allow for ridges, hips, and waste, it is advisable to add 10% of your final roof area for a gable roof or 17% in the case of a cottage roof.

As a result, you should be working with 1,386 sq. feet or 1,474 sq. feet for a gable roof or a cottage roof respectively. Get to know more about us!

Know Your Roof Type

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Just measure the length and width of each plane on the roof, including dormers. Then, multiply length x width to get the square footage of each plane. Simply add the square footage of each of the planes together to derive the total square footage of your roof.

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What Is The American National Standards Institute Method For Measuring Square Footage

While a national standard for measuring square footage is not currently in place, an organization called the American National Standards Institute provides guidelines on how to calculate the square feet of a house, which many real estate agents and homeowners follow. The ANSI method encourages calculating square footage from the homes exterior, but the wall width is not typically subtracted to account for actual living space. Many condominiums do not have square footage guidelines in place and do not always follow ANSI guidelines.

How To Calculate Square Feet Of A Roof

How To Calculate Square Footage Of A House Roof

Before you do any roofing work, you must calculate the roofs square footage to determine how much material you need. Shingles and other roofing materials, such as underlayment, are typically measured in squares that are 10 feet long and 10 feet wide, with each square measuring 100 square feet.

When calculating square footage for your roof, always add at least 10 percent of the total to account for waste.

  • Measure the length and width of every roof plane or surface. Include dormers . This information may be available on the homes original building plan or, if the roof surface is relatively low and flat, you can measure it yourself. If you cannot get up to the roof and measure safely, either hire a professional or make your best estimate of the roof surface dimensions.

  • Multiply the length and width of each square or rectangle-shaped plane. Calculate each plane separately. For example, if one roof plane measures 120 feet by 120 feet, 120 x 120 = 14,400 square feet.

  • Calculate the square footage for symmetrical, triangle-shaped planes by multiplying the length of the triangle’s base by its height . Then divide the total by 2 to get the square footage. For example, if a triangle-shaped roof plane measures 60 feet along the base and is 30 feet high, we have 60 x 30 = 1,800 feet, divided by 2 = 900 square feet for the triangle-shaped plane.

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    How To Measure A Roof For Shingles From The Ground

    Remember when your high school algebra teacher said you needed to know how to calculate slope. He may have been thinking about measuring the square footage of a roof.

    This method allows you to calculate roof slope and determine the roof area while keeping both feet firmly on the ground.

    Begin by measuring the distance from the edge of the eave to the point at which you can barely see the slope of the roof. This works best if you can attach the tape measure to the eve, then walk to the appropriate place and take the measurement at eye level.

    This measurement is the horizontal run of the roof. Now, stand under the gutter of the roof you are measuring the slope for and measure the distance from your eye to the roof overhang. This is the roof rise.

    Divide the roof rise by the horizontal run to get your roof pitch. For example, if the rise is 60 inches and the run is 120 inches, youll have a roof pitch of 6/12.

    As in the method described above, measure the length of the roof from the edge of one eave to the other and the width from one eave to the other. For example, a roof that measures 60 feet by 40 feet would be 2,400 square feet.

    Next, use the table below to determine the slope factor. In our example, the 6/12 roof would have a slope factor of 1.118. In our above example, you would multiply 2,400 square feet times the slope factor to get the total square footage of 2,683 square feet.

    Square Footage Information Changes Depending On The Source

    The real estate listing has a home square footage number, but no basis on what this represents. The property appraiser has a square footage number, but they are only looking at your property tax liability. You have a number in your mind from when you bought the home, or a round-a-bout number that you may have used in other projects, but is this number even accurate? The numbers you have may only be air conditioned space, because isnt that what is most important?

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    Estimating Materials Based On Actual Measurements

    Measuring each roof plane requires you to actually go onto your roof. If your roof has a number of planes and numerous hips, ridges and valleys, this is the most accurate way to calculate the materials needed. Take a metal tape measure and a pen and paper. Measure each planes length and width. Record your measurements. Once you are safely on the ground, use your measurements to determine the square footage.

    For rectangular areas, multiply the length by the width. For example, if a plane measures 30 feet by 100 feet, this would be 3,000 square feet. For triangular areas, you may need to dust off your geometry book. If the area forms a right triangle, you can make use of the Pythagorean theorem. Otherwise, you might want to look up how to calculate the semiperimeter and then use Herons formula to find the area. Be sure to add extra for valleys, hips and ridges.

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    Calculate The Square Footage Of The Roof Area With The Roof Pitch And Base Area

    How to measure a roof and calculate square feet. | 01/2020

    Find your roof pitch from the first step in the following table and multiply the amount you just got by the corresponding roof pitch multiplier. The result is the total roof square footage youll need to get roofing material for.

    In our example, the roof pitch was 6/12. The pitch multiplier would be 1.118. So, take the 2,100 square feet, multiplied by 1.118 to get 2,347 square feet of roofing material. Since roofing material like shingles come in squares of 100 square feet apiece, wed need at least 24 of them. If you have a relatively flat roof , you can simply avoid using a pitch multiplier and make sure to round up on your equipment estimate.

    Roof Slope


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    What Is Considered In A Homes Square Footage

    Only finished spaces are included in a homes square footage. Finished spaces include any area that can be lived in throughout the year, and typically has the following attributes:

  • Ceiling

  • Wallcovering

  • Flooring

  • Heating and cooling

  • The rooms that are typically included in a homes square footage, if they are finished, include:

  • Living room

  • Detached in-law quarters

  • Two: Split Tricky Shapes Into Squares And Rectangles

    Once you have these figures, return to the safety of your home. Notice in the image above that the hip roof is made of two triangles and two trapezoids. Trapezoids are tricky to get the area measurement of, so were going to split each of them into two triangles and a rectangle:

    We know enough about the overall measurements of the roof to fill in the missing values. Lets fill the figures in now:

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    How To Measure Your Roofs Square Footage

    The square footage of your roof has a huge impact on the cost of your replacement. It affects a number of cost factors, including the amount of materials used, labor, and time.

    Be aware, the only way to get a 100 percent accurate measurement is to have a local roofing contractor come out to professionally measure your roof and give you a quote. However, I can give you the calculations to get a rough measurement of your homes square footage.

    The Labor And Time To Complete The Job

    Roofing Calculator

    Labor and time are two of the main factors a roofing contractor considers when calculating the price of your new roof. If anything takes time and labor, it will show up in the final cost of your roof replacement.

    The labor cost of each man on a crew is based on their skill level, experience, and how much they can get done in a day. The labor cost will vary from contractor to contractor.

    The time it takes to complete the job is also a factor. The more time a roofer has to spend on your roof and property will always affect the price of a new roof.

    If the roof is complex and hard to access, it take longer and more labor to complete. From tearing off your old roof to cleaning up your property after the job is done, if it takes manpower and time, its going to impact the cost of your new roof.

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    How Many Rolls Of Felt Will You Need

    Roofing felt is sold by the roll. The average roll of 15-pound roofing felt covers about 400 ft2, or 4 squares, while the average roll of 30-pound roofing felt covers about 200 ft2, or 2 squares.

    Rolls of felt are 36 wide x 144 long for 15# and 72 long for 30#. Consider other underlayment options as needed, such as rubber or tar products.

    How Many Bundles Of Shingles Per Square

    A package of roofing shingles is called a bundle. Laminate or architectural shingles, one of the most common types of roofing shingles, are generally packaged in three bundles per square.

    So in the 2400 square foot gable roof example, you would need 72 bundles of shingles .

    Here are a couple more examples:

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    How Do I Measure A Steep Roof

    Most roofers wont go on a roof with an 8/12 roof pitch or greater with special equipment such as scaffolding and roof jacks and neither should you. Instead, use one of the four methods described above that allow you to measure the roof while standing safely on the ground or from the comfort of your computer.

    While these methods may not be quite as accurate as taking actual measurements from the rooftop, theyre close enough for calculating how many shingles youll need to purchase for a new roof.

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    How Do I Calculate Roof Pitch

    How to measure roof sections both from on the roof or from the ground

    While using a roof gauge or the sight method described above are two ways of measuring roof pitch, if you have an attic, theres an even easier method. Head to the attic with a level and tape measure and choose a rafter.

    For example, if the vertical measurement from the level to the rafter is 6 inches, the roof has a 6/12 pitch.

    If you have a smartphone, you can also download one of several free roof pitch apps, such as Pitch Gauge. These apps allow you to determine the roof pitch simply by holding the phone against the roof or the rafter.

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    How To Calculate A Roofing Square

    Before beginning, make sure you can safely access your roofif you can’t, contact a roofing professional for help.

    Grab your measuring tape, level, pen and paper, roof safety equipment, and your ladder. With these in hand, you can measure your roof in five simple steps.

  • Determine the number of planes. Your roof is made up of planes. If you have a flat roof, it has one plane. If you have a simple gable roof, it has two planes. The more architectural details your roof has, the more planes you will have to measure.
  • Measure each plane. Find the length and width of each plane. Then, multiply those two numbers together to find the square footage of that plane. For example, a 35 ft. X 36 ft. plane = 1260 sq. ft.
  • Find the total of all the planes. Add the square footage for each roof plane into one total. 1,260 sq. ft. + 1,260 sq. ft. = 2,520 sq. ft.
  • Divide to find the squares. To find how many squares are on your roof, divide the total square footage of all your planes by 100. In our example, the total was 25.2 squares 2,520 sq. ft. divided by 100.
  • Remember the roof slope. Roof slope indicates how steep your roof is and may increase the number of squares of materials you need. Roof slope is calculated by determining how many inches a roof rises vertically for every 12 inches it extends horizontally. For example, if that vertical rise is 4 inches, the slope is 4:12.
  • What If You Have A Steep Roof

    To measure a steep roof, use one of the following alternate methods:

    Method 1

    Calculate the roof length by measuring the exterior walls plus the overhang for the length of the house parallel to the ridge.

    Next, throw a rope over the ridge and mark it where it meets each eave. This will give the width dimension to use in figuring your area. This should be done on each roof section containing a horizontal ridge.

    Method 2

    Determine the roof area by using a mathematical formula that accounts for the roof length, total span, and roof pitch:

  • Determine your roof pitch by using a pitch gauge or a smartphone app .
  • Measure the length of the roof surface, including overhangs.
  • Measure the span of the roof, including overhangs.
  • Multiply the length x the span. The result will be the plane area. Use the chart below to calculate the total area of the roof.
  • Calculate the total roof area Plane Area x Correction Factor = Roof Area
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    How To Measure Your Roof From The Top Of The Structure

    The most accurate way to measure your roof is by being on top of the roof itself. You can make sure each roof sections slope area is accounted for. Youll need some graph paper, measuring tape, and a calculator. For our example, well use a hip roof, though you can use this technique to measure any shape roof with varying complexity.

    Figure Out Your Homes Footprint


    If you use the square footage of your home, youll only get a vague idea of what the square footage of your roof is. Thats why you have to figure out your homes footprint.

    A person of average height will have a stride somewhere between 2 to 2.5 feet. To figure out your homes footprint, you can step off the dimensions of your roof by counting the steps you take to get the length of your home. You will then step off the width of your home.

    After stepping off the length and width of your home, youll multiply the two numbers to get your homes footprint.

    Length x width = your home’s footprint

    Your calculations are going to be off, but measuring this way can give you a basic idea of your homes footprint. Keep in mind, square footage of a house does not equal the square footage of a roof.

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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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