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How Do I Calculate Roof Square Footage

Tips For Getting Started

How to Measure the Square Footage of a Roof

Tip 1: Measuring to the nearest inch along eaves and across gables can be done from the ground just dont forget the overhang.

Tip 2: If you know the dimensions of your previous asphalt roofing job, you can use this info to cheat a little. Typical 3 Tab asphalt shingles have tabs that are 1 foot wide with a vertical exposure of 5 inches. Make sure to physically verify these dimensions by measuring 4 or 5 courses. Counting the shingles can give you eave to ridge dimensions from the ground.

Tip 3: 100 Square Feet = 1 Square in Roofing Terms

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.

Calculate The Surface Area Of The Roof

Take the areaof the roofs footprint, say its 5,000 square feet, and multiply 5,000 by 1.118.

That gives you 5,590 square feet, which is the actual area of the surface of the roof. And thats what you were looking for.

This applies to rafter lengths as well as areas. A rafter for a roof with a 6:12 slope will be 1.118 times as long as the horizontal length that it covers.

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Roof Slope Multiplier Chart

We also have a much more complete roof slope multiplier chart that includes slopes by the half inch and slopes up to 30.5-in-12.

If youre using the table below, you should consider getting yourself a construction calculator. That way you can instantly calculate the factor for any slope, among many other useful things. This one is very good.*

Roof Pitch

Types Of Roofing Quote Material

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From asphalt shingles, flat roofing, metal roofing, and concrete tile roofing, there are a myriad of pricing differences and waste factors that go into each individual price structure of a project for each different product. Not limited to slope of roof, hip footage, ridge footage, valley footage, edge footage, field footage, access, number of stories, and job location all have to do with it. Usually we can get an idea just knowing the roof field footage and the slope, but it is not something that is across the board, at least not for us. There are some companies that have set per square foot pricing, but we have not found this to be efficient. If we paid our guys the same on an easy up and over roof that we did on a cut up and steep one, do you think the workmanship will be the same? I dont think so, and the latter is the one that needs the excellent workmanship just to survive.

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Expressing Roof Slope In Degrees

The rest of the English-speaking world uses degrees, which seems simpler, but it takes a few extra steps to figure it out mathematically.

It also doesnt immediately convey as much information about the roof on a practical level as the rise-in-run ratio expression.

To express the slope in degrees, you divide the rise by the run and find the inverse tangent of the result.

But you still need to know the rise and the run to find the roof slope in degrees unless youre using a slope finder that tells you the slope in degrees.

What About The Waste Factor Should I Order Extra Roofing Materials

You want to order extra material to account for waste. Waste factors vary.

10%-15% is a good rule of thumb, but your results may be different. More complicated roofs will have a higher waste factor because there are usually more cut shingles around corners, walls, and edges.

It is okay to have a few shingles left over. They can be saved in case there is roof damage later or if repairs need to be done in the future.

So for the 24 square roof example, you would want to add 2.4 squares which equal about 7 or 8 more bundles.

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S To Calculate Your Roofs Square Footage

You just learned what a roofing square is. The number of roof squares has a huge impact on the cost factors, such as the amount of materials used, labor, and time.

Before investing in a new roof, wouldnt it be great to know how much itll cost per square?

If you answered yes, we have a great way to roughly calculate your roofs square footage to give you an idea of the cost of your new roof. 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.

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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 × 15 = 750 square feetS3 = /2 = 135 square feet

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Find The Area Of The Roofs Footprint

Determine the areaof the roofs footprint, which is the area covered by the roof regardless of slope .

Google Earth makes this pretty easy, but you can also simply measure the dimensions of the building on the ground and figure out the area that way .

Dont forget to take into account overhanging eaves or any other areas where the roof extends beyond the exterior walls of the building.

You will also need to increase your total footprint area to include any areas where one roof section overhangs another roof section.

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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Get A Budget Roofing Quote That Means Something

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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How Many Shingles In A Square Of Roofing ...

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Find The Area Of A Roof

Multiply the length of the roof in feet by the width of the roof in feet to find the area of the roof in square feet. If you have multiple sections of roof find the area of each and add them together to find the total area.

If your roof is not flat and you cannot climb to the peak to get accurate width measurements then you can add a multiplier for the pitch of your roof.

Use our roof pitch calculator to find the pitch of your roof or find the pitch multiplier, then multiply the area of the footprint of your roof by the multiplier to find the actual area.

Alternatively, find the area of your roof using our roofing calculator, which can also estimate shingles and material needed for your project.

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For example, if your roof is 30 ft by 50 ft, then the area is 1,500 ft2.30 × 50 = 1,500 ft2

If your roof has triangles and other shapes youll need to use a calculator to find the square footage.

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 havethe 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 youhave 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 slope, you can use it to find the actual area of any size roof with 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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Roofing Quote Footage Is Not The Same As Home Square Footage

Depending on where the information is coming from is going to determine the basis on which the estimated roof footage is calculated. The roof square footage is what we need to calculate a budget quote to do the job. So when you say my home is 1,500 square feet, how much to do the roof? Well, that is a good question. Does that amount include the garage? Does it include the back covered lanai area that is encompassed in the main portion of the roof? Does it include the addition that was built last year? Does it include the 2 4 overhang or soffit area? Does it include the front entry? All these things could add much square footage to that 1,500 sq. ft. number. It also does not encompass all that is needed to come up with the square footage of the actual roof. This does not automatically mean the roof is 15 squares, as some might lead you to believe.

Convert Among Square Inch Square Foot Square Yard And Square Meter

How To Measure The Square Footage Of A Roof With Google Earth. Measure A Roof For Metal Or Shingles.

You could, for example, perform all of your measurements in inches or centimeters, calculate area in square inches or square centimeters then convert your final answer to the unit you need such as square feet or square meters.

To convert among square feet, yards and meters use the following conversion factors. For other units use our calculator forarea conversions.

  • Square Feet to Square Yards
  • multiply ft2 by 0.11111 to get yd2
  • Square Feet to Square Meters
  • multiply ft2 by 0.092903 to get m2
  • Square Yards to Square Feet
  • multiply yd2 by 9 to get ft2
  • Square Yards to Square Meters
  • multiply yd2 by 0.836127 to get m2
  • Square Meters to Square Feet
  • multiply m2 by 10.7639 to get ft2
  • Square Meters to Square Yards
  • multiply m2 by 1.19599 to get yd2
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    What Is A Roofing Square

    Roof surfaces are measured in squares.

    A roofing square is equal to 100 square feet of the roof.

    To determine the number of squares on the gable roof example in this post, divide its total of 2400 square feet by 100 .

    This means you would need 24 squares of shingles to cover that roof. Be sure to add 10%-15% to all your material totals for trim allowance .

    Pro Tip: Want to skip doing some math?Order a FREE RoofScopeX aerial roof reportto see the size of your roof in squares, as well as the slope of your roof. Keep the report on hand for future conversations with roofers or when reviewing estimates for your next roof replacement or repair.

    Ready to get an estimate?

    Search our list of independent roofing contractors in the Owens Corning Roofing Contractor Network to find the roofing professional thats right for you.

    Estimating The Cost Of The Roof

    Once you know the area of the roof, you have to decide on the scope of works. Do you want to build the roof from scratch, or maybe replace the old layers? You also need to decide on the finishing material. For example, asphalt shingles will be less expensive than clay tiles.

    After you’ve made all of these decisions, it’s best to contact your local contractor and ask about the cost of both materials and labor per square meter or square foot of roof area. Remember that this unit price should include all additional elements such as fasteners, as well as the cost of removing all layers and disposing of them .

    The most typical cost of roofing falls between $2 and $4 per square foot . If the price proposed by your contractor deviates from these values, it is advisable to check with other contractors before starting the works.

    If you cannot contact any contractor, calculate the cost of materials and multiply this price by 2.5. You will obtain an approximate price including labor, assuming that 40% of the cost is taken by the materials and 60% by the labor.

    The last thing you have to do is to multiply this cost by your roof area and voilà, you now know the total cost of your roof! Remember that the real cost might differ from this value a bit due to waste, so plan ahead and assign more funds to this construction work.

    Make sure to take a look at our concrete slab cost calculator, too!

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    Calculate The Square Footage Of A Gable

    To calculate the square footage of a gable wall section, you need to know the wall length and the height of the gable. If for some reason you can’t get the height of the gable, you don’t have a ladder long enough, or you are one of those that should not be at heights if you know the pitch of the roof and the wall length, you can also calculate the square footage of a gable.

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

    Roof squares and quantity

    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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