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How To Calculate Square Feet Of A Roof

Estimating Materials Based On Actual Measurements

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

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 Complex Roof Areas

Most roofs in Canada would be considered on the complex side. Multiple adjacent pitches, dormers, and turrets are common. Keep in mind that an experienced metal roofing contractor will need to factor in extended labour time for areas of your roof that will require precision metalworking skills.

Start by finding the footprint area and multiply by the correct slope factor determined by pitch . In Figure 4 below, the dashed blue lines give a simplified view of the footprint. Multiply L x W to calculate the area for each rectangular section. Note the area of 77ft2 that needs to be subtracted for the recessed area.

Once the footprint including overhang areas have been determined for each area, find the appropriate slope or pitch factor in the chart below. For example, a roof area with an 8/12 pitch has a slope factor of 1.202 so 2053ft2 x 1.202 = 2468ft2 total roof area.

A Note about complex roofs: Complex roofs need more accessories and trims thaneasy roofs resulting in a slightly higher total cost/square foot.

Figure 4. Calculating Complex Roof Area

How To Measure Roof Rise

Typical vinyl siding has 4 exposure, so 3 spans would be equal to 12 or 1 foot. Calculate the number of spans from the base line to the peak. Since most homes have a Rake wood, which is usually 6-8 wide, you can add that width to the rise.

Example: If you have 19 spans of siding at 4 exposure of each span, and a 6 rake board, the rise would be:

/ 3 = 6 10 roof rise.

Converting pitch to degrees can be useful in figuring out the roof geometry, or for European contractors who are not accustomed to th eUS system. See Table below:

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Recommendation Of How To Calculate Square Footage Of A Roof

The construction process likes precision. To correctly build and lay a roof firstly it is necessary to understand all nuances of how to calculate square footage of a roof.

Very often people decide to make a roof and a house itself on their own. In this case they should definitely know how to calculate square footage of a roof. In the space calculation you must be especially careful, since with the wrong approach you risk not only to get an ugly structure appearance, but also spend money for the purchase of excess materials.

Roofing Squares: A Way To Measure Your Roof

How to Measure and Estimate a Roof Like a Pro?

So youve decided to re-shingle your roof, youve called the contractor and all seems well until the contractor comes down and you hear a term youre not familiar with, roofing square

What? you ask yourself, wondering what exactly the person you hired just said to you, did they mean a square foot, a panel, something else entirely? Dont worry, youre not alone. Its a question we at Rennison Roofing get all the time!

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How Much Does Roofing Cost Per Square

The amount you will pay for materials per square can depend on several factors. The type of materials and the scope of the project can make the cost range drastically. However, you will typically be looking at $300 to $500 per square for shingle installation. You may pay a little more for specialty shingles or tiles.

Translating The Cost Of Roofing Squares

Some homeowners find the concept of a roofing square confusing and would prefer to see their roofing cost broken down by square footage. If youre in this boat, all you need to do is divide the cost per roof square by 100 to learn the cost per square foot. For example, if your roofing contractor tells you the cost per square is $500, then that comes down to $5.00 per square foot of your roof. This might help you better understand the approximate cost of your roof replacement project.

When you work with Long Roofing, always feel free to ask questions about your roofing upgrade. If there is any confusion with the terms of your roof estimate, we welcome you to ask us to explain the estimate so you fully understand the value of your investment. We want all of our customers to feel knowledgeable and comfortable with their home improvement projects. If that means explaining the process better, our team is happy to do so.

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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?

Roof Square Footage Calculator

How to Measure the Square Footage of a Roof

While it is good to know how to do the calculations yourself, there is a much easier way: a calculator! You can just put in the length, width, and pitch of the roof. Once you plug them in, it will calculate the squares and amount of supplies that you will need to redo the roof. You can even use it to calculate only a portion of the roof to determine the number of materials needed for a smaller project.

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

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


Find The Area Of The Footprint Of The Roof

To calculate a roofs dimensions, you need to measure the roof as if it were flat, then account for roof pitch, calculate square footage, and finally determine how many squares of material are required for the roof.

The calculator above can handle all of this, simply enter the length, width, and pitch, and it will determine the size of the roof in squares.

Start by measuring the roofs length and width in feet as youre standing on the ground. Remember that the length and width need to be found for the roof, not the house, so take into account that the roof overhangs the building.

Then determine the area of the roof as if it were flat. Multiply the length by the width in feet to get the area measurement.

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Below, there is a simple triangle, and the math used to work out how to make a proper measurement. Once you work through the basic triangle, we will review a typical roof, and how to apply some simple math to calculate how much material you will need for a roof used in our hypothetical example.

1 roof square = 100 square feet The length times the height of a triangle is twice its area . So if you divide your answer of a product of length times height by two, you will get the area of a triangle. /2 = Area

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In Figure above: l=30 feet h=12 feet /2 = 180 square feet

Now that the basic concept has been covered, lets take a look at a more complex roofing system. In this overhead view you see both a hip-end section, and gable ends. With a more complex roof such is this one, it is highly recommended that you make a basic sketch. By doing so, it will be easier to mark your measurements, and calculate the necessary materials for the project. For this example we will break this roof up into sections labeled A through E.

In the figure B. above, a sketched portion is a basic triangle. As we did in the first example, measure the length of the eaves, and the vertical line from the eaves half way point to the peak. Multiply these numbers, and then divide the answer by two./2 = 270 square feet

S1 = /2 = 135 square feetS2 = 50 Ã 15 = 750 square feetS3 = /2 = 135 square feet

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Two: Split Tricky Shapes Into Squares And Rectangles

How to Calculate Roof Square Footage? What

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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Calculate The Roof Area

Now that you have all of your roof measurements, you can calculate its surface area. Simply multiply the length and width of each rectangular plane, and then add the combined area of the hips. Then multiply this number by the roofs slope factor, and then multiply this final result by 1.10 to allow for error.

In this example, our imaginary home’s hip roof would cover a surface area of + , while the lean-to roof would be equal to . This gives you a total surface area of 935 square feet. Multiplying this by the slope factor of 1.03 equals 963.05 square feet. Multiply this by 1.10 to obtain 1059.4, which is a good estimate of your roofs surface area.

Square Feet To Roofing Squares

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Unit Descriptions
1 Square Foot:
Square foot is an area of one foot by one foot. One square foot = 144 square inches = 1/9 square yards. In SI units a square foot is 0.092 903 04 square meters. 1 sq ft = 0.09290304 m2
1 Roofing Square:
10 feet by 10 feet = 100 square feet. Using an international foot of exactly 0.3048 meters length. 100 Square feet = 1 Roofing square = 9.290304 cubic meters . 1 Roofing square = 9.290304 m3.
Link to Your Exact Conversion

Similar Area Units

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How To Use Pitch Calculator

To estimate roof area, enter width and length , and either Rise or Pitch second value will auto-calculate. Click calculate. The results will pop up below the calculate button, and will include: Rafter Length, Total Size / Area, and Pitch.

Using the diagram below, measure your roof from the ground, and enter building dimensions into the calculator #2 above. Enter the span , and the rise above the base line.

To calculate your pitch and size, measure your roof and plug in your measurements in accordance with the diagram below. Enter EITHER Roof Rise or Roof Pitch.

Finding The Total Roof Area

How To Calculate Roof Area

Once the area of the roofs footprint is known, the overall roof area can be found by accounting for the roofs pitch. The pitch of the roof is the rise over a 12-inch run. Use our roof pitch calculator to find the pitch of your roof.

Next, multiply the footprint of the roof by the multiplier below for your roof pitch to find the overall roof area.For example, a 4/12 pitch roof that is 100 square feet:

100 × 1.054 = 105.4ft2

Roof Pitch Area Multipliers

Multipliers for common roof pitches that can be used to find the total area of a roof.


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Determine The Roof Slope Multiplier

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

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.

Estimate Your Home Footprint

While you can take a measuring tape out to get the measurements of your homes footprint, you can also roughly estimate it with your steps. On average, an adult person has a stride somewhere between 2 and 2.5 feet. Step around your homes length and width to find the dimensions of your roof, counting your steps for an estimate.

Write down your measurements, marking the length and width. Multiply these numbers to get the home footprint.

Note: even if you use a measuring tape, these measurements are an estimate. Your homes square footage isnt necessarily the same as the square footage of your roof.

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What Roof Type Is Best Suited For Your Roof Pitch

If you have roof pitch of 3/13 or lower, it is highly recommended that you use/install a flat or low slope roofing .

If your roof slope is above 3/12 , you can install either asphalt shingles, or a metal roof, or one of the exotic roof types: Slate, Tile, Wood, etc.

Metal roofs have the highest wind blow-off resistance, and are best suited for ice dams prevention especially if your roof slope is below 6/12!

Get A Budget Roofing Quote That Means Something

How To Calculate Square Footage Of A House Roof

So now when you call your favorite roofing service provider, you can ask them to give you a budget quote based on an internet measurement. When the roofing company starts asking those nosy questions like what is the address? How many stories is this home? What kind of roof are you wanting to put back? Are you the current owner? You will know why they are asking. Some roofing companies use pay services to get satellite takeoffs for their roofing quote, and they are very detailed. For homes that are just looking for a number, this is just not cost efficient for the roofer. They are usually more cost efficient for the very large homes and commercial type properties.

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