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How Many Square Feet Is My Roof

Roof Slope Multiplier Chart

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

Since the roof slope multiplier is so important to estimating the area of a roof, weve put together a quick reference 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 to help you figure out the area of a roof, 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

Notes On Calculating The Area Of A Roof

  • Ifthe roof has areas with different slopes, as on a gambrel roof, youll have to figure out more than one slope and use the appropriate roof slope multiplier for the different areas.
  • As a shortcut, the roof slope multiplier for any slope can be determined by finding the square root of ² + 1).Divide the rise by the run. Square the result. Add 1 to the result of that. Find the square root of that result.
  • If you knowthe roof slope in degrees, simply find the secant using a scientific calculator. For example, if the roof slope is 45°, then sec = 1.414213. Thats your roof slope multiplier.
  • Convert All Of Your Measurements To Feet

    • If you measured in feet skip to “Calculate the Area as Square Footage”
    • If you measured in feet & inches, divide inches by 12 and add that to your feet measure to get total feet
    • If you measured in another unit of measure, do the following toconvert to feet – inches: divide by 12 and that is your measurement in feet – yards: multiply by 3 and that is your measurement in feet – centimeters: multiply by 0.03281 to convert to feet – meters: multiply by 3.281 to convert to feet

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    How Many Nails Will You Need

    Nails will also be required for any roofing project. The average 3-tab shingle needs four nails per shingle. High wind areas and other types of shingles may need more. 320 nails will be needed to install a square of standard 3-tab shingles, assuming four nails per shingle and 80 shingles per square.

    Measuring Or Calculating Gable And Hip Lengths

    How Many Shingles In A Square Of Roofing

    The slope factor is also used to determine gable lengths when the run length is known. For example, in Figure 4 the bottom left gable measures 16 across from eave to eave and therefore has a run of 8. When this is multiplied by 1.202 the gable distance is 98 . Note that this run can also be multiplied by the hip/valley factor of 1.563 to get a valley length of 126.

    Record all your calculations on your drawing as seen in Figure 5 below.

    Figure 5. Completed Roof Plan Drawing

    Pro Tip: A Note About Waste Factor

    Once you have figured out your roof area, you will need to also calculate how much room you need to allow for waste. For metal roofing products on a medium complex roof a waste factor of 15% is advisable. In other words for the 2468 ft2 roof in our example you should multiply by 1.15 giving you 2838.2 ft2 roofing material needed.

    Important Note: Most metal roofing products are packaged and sold by the square so for our example roof the number of squares or boxes to purchase is 29.

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    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.

    Convert Among Square Inch Square Foot Square Yard And Square Meter

    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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    How Many Shingles Are In A Square

    When the time comes to buy shingles for your roof, keep in mind that they are usually sold by the bundle. Each bundle is a wrapped package of shingles with such a weight as to be lifted easily by a person.

    The most common is to have three bundles of shingles for a square of roof area. In other words, if you buy 3 bundles of shingles, this will cover one square which is 100 sq.ft of area.

    The most usual case when buying standard shingles , there are 29 standard-sized shingles in each bundle.

    Summary of the above:

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    Gable Roof Sheathing Calculator

    How Many Square Feet Is My Roof?

    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 4′ x 8′ size. 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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    Find The Slope Of The Roof

    Before you can determine the area of a roof, you need to know its slope. You can find the slope by getting up on a ladder at the rake edge of the roof and measuring with a ruler and a spirit level, or you can use a specially-designed slope finder.

    Measuring roof slope with a bubble level and a ruler. This level has no measurement markings, so the yellow tape is being used to mark 12 inches from the end of the level that touches the roof. This roof has an 11-in-12 slope.

    You could also take your measurement in the attic using the underside of a rafter, the underside of the roof sheathing, or even the ceiling, if youre sure that it follows the slope of the roof.

    Eyeballing the slope and guessing is probably not a good idea.

    The result you get from guessing like this might be close enough for government work, but if its a large roof and youre a roofer with a 10% profit margin, I wouldnt recommend it.

    There are also a number of smartphone apps that you can use to find the slope of your roof, if you have a clear view of a gable end on the building. These can be acceptably accurate sometimes.

    You dont have to get up on the roof or go to the attic to use these. Go search in your app store for roof pitch apps. Youll see.

    Measuring roof slope with a slope finder.

    How Big Is A Square In Roofing

    The calculations above will give you the total number of square feet of the roof area.

    As you have noticed in the roofing industry however, the surface of the roof is being measured in squares. This refers to the roof area that measures approximately 100 square feet.

    Therefore: 1 Square in Roofing = 100 square feet

    Now, in order to determine how many squares are there on the gable roof for example, all you need to do is divide the total square footage by 100.

    • Total square footage from Example 2 above: 28,000 sq. ft.
    • Number of squares for 2 planes: 28,000 sq. ft. ÷ 100 = 280 squares

    This means that both planes of the roof will require 280 squares of shingles. A three-tab shingle, which is most commonly used, is packed in 3 bundles per square.

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    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.

    How Do Solar Installers Design System Layouts

    How to Get Your Estimate Using The Roofing Cost Calculator

    Hereâs a secret: most solar installers use a method similar to the one described in this article to prepare system layouts for customer quotes. While they use professional software, solar companies almost always make use of satellite images from Google Earth or other sources as a starting point.

    A responsible company will always come to your house to ground-truth the design by verifying measurements and looking for issues that arenât always visible in satellite photos like vent stacks, shading, and roofing issues.

    But pretty much all solar installers start the design process by using satellite images. Hereâs how you can do a rough draft yourself.

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    The Operating Cost Of Your Roofing Contractor

    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.

    Looking Up At Your Roof And Wondering How Many Panels You Can Fit Up There Heres A Method That Doesnt Require A Ladder

    If you used The Solar Nerd calculator, youâll have an estimate of how many solar panels you need to generate all of your electricity. But then the question is: will that many panels actually fit on your roof?

    You might know the square footage of your house, but that doesnât tell you the area of roof thatâs available to fit solar panels. What you want is a big rectangular area without any shade. A south or west facing roof is usually best, but east can be viable in some cases.

    But not all rooftops are simple rectangles. Hip, gabel, and mansard roofs, for example, are designs common on American homes, and they each have a different geometry that changes the amount of usable area. So do features like dormers, ventilation pipes, and chimneys.

    Another possible situation is that you have a good amount of roof area, but itâs shaded by trees or neighboring buildings.

    Finally, you may have local fire setback codes that require you to leave a free pathway on the edge of your roof for access to firefighters.

    All these considerations will affect what the final layout of your solar panels will be, which is why you want to work with a professional installer to give you a design proposal. But with the method Iâll describe in this article, you can make a decent estimate of your solar panel layout in just a few minutes.

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    Disclaimer About This Tool

    Of course, the methods described in this article for making a rough calculation are just to give you a quick way to figure out how many panels you might be able to fit on your roof. Itâs no substitute for working with a professional solar installer who will include a site layout with your solar quote and explain in detail which sections of your roof are best suited for solar panels.

    Theyâll also be able to identify obstructions, shading, and other issues.

    When youâre ready to work with a professional contractor for your home solar panel installation, fill out our form to get quotes from up to three qualified solar installers.


    How To Calculate A Roofing Square

    How to Measure the Square Footage of a Roof

    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.
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    Is A Roof The Same Square Footage As A House

    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.

    How Do You Calculate The Roof Square Footage Of 1500 Square Feet House

    Figure out the area of the house plus overhangs:- determine the squre footage of the shed foot print by measuring the length and width of the shed including the overhangs. Assume the overhangs are 1 feet both sides eves and rake then you have 2 feet extra, so each dimension for 30×50 = 1500 sq ft with overhangs is around 32×52 = 1664 square footage.

    Find the roof pitch or slope:- the roof pitch is the amount of slope. The slope is described by the rise in inches or how far up it goes over the run in inches or how far horizontal it goes. We will use a 4 in 12 pitch. For every 4 inches the roof goes up to the peak it goes 12 inches horizontally.

    Calculate the square of rise and run and sum it:- square of rise 4×4=16, square of run = 12×12 = 144, add both 16 +144 = 160.

    Find the square root of the sum:- square root of 160 = 12.649

    Sum divide by 12 to get the product:- square root of 160 = 12.649 is divided by 12 as 12.649 ÷ 12 = 1.054, hence 1.054 equals the product

    Multiply the product by the flat roof area and divide by 100:- our house is 1500 square footage which as 1664 sq ft with overhangs, so 1.054 x 1664 = 1754 square feet, 1454 / 100 = 17.54 squares.

    Add 10% for wastes and starter:- wastages 10% of 17.54 squares = 1.754, so final squares of shingles do you need = 17.54+ 1.754 = 19.294 squares, it is rounded to 19 squares.

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    Calculate The Square Footage Of Your Roof

    Now that you thought about the slope and complexity of your roof, youre ready to learn how to calculate the square footage of your roof.

    To get a rough estimate for your roofs square footage, youll use this equation:

    For example, if you have an easy up and over, walkable gable roof and a house that measures 56 feet lengthwise and 28 feet widthwise, your calculation will look like this:

    1,568′ =

    x 1.3

    2,038 = square feet of roof area

    Using this equation wont be 100% accurate, but knowing your roofs square footage is a great jumping-off point to learn how much youll have to invest in your replacement.


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