How to Measure the Square Footage of a Roof

How to Measure the Square Footage of a Roof

There are two ways to estimate the total
number of squares that are installed on the roof. One way includes measuring the
area of the house footprint and multiply that by a roof slope factor. Another way
includes measuring the area of each plane on the roof and add them all
together. In this video, we’re going to learn how to measure each plane of the
roof to calculate the total square footage. To do this, you have to measure
the length and width of each plane on the roof including the dormers then
multiply length by width to get the square footage of each plane finally
calculate the roofs total square footage by simply adding the square footage of
each of the planes together there are several different styles of roofs
including shed roofs hip roofs and gable roofs this is a shed roof a
shed roof has one roof plain simply measure the length of a then measure the
length of B now the area of the shed roof is a times B which is in this
example twelve and a half feet times twelve and a feet which is 156 in a
quarter square foot for the total square footage of the shed roof this is a
square the area of a square is simply base times height in this example the
base is twelve and a half and the height is twelve and a half this is a rectangle
the area of a rectangle is just like a square it is base times height and in
this example the base is 15 feet and the height is 12 and a half the area of the
rectangle is therefore 15 times 12 and a half which equals 180 seven and a half
square feet this is a gable roof a gable roof has
two planes so multiply the base times the height for each plane or rectangle
to get the square footage for each plane then add the two rectangles together to
get the total square footage of the roof so let’s assume one rectangular plane of
the roof is sixteen by 40 and the other plane is sixteen by 40 the area of each
plane is 16 times 40 equals 640 square feet by adding the two rectangular
planes together the total square footage of the roof is 1280 square feet this is
a hip roof now a hip roof has four planes and they are not rectangular like
the other roofs so you’ll need to know some simple geometric formulas to
calculate areas of roof shapes including trapezoids and triangles a hip roof will
include a trapezoid shape to calculate the area of a trapezoid you add the
length of each base base one plus base two and then multiply it by height then
you divide that by two to get the square footage of the one trapezoid plane in
this example one of the hip roofs trapezoid planes is 10 plus 15 times 12
equals 300 divided by 2 equals 150 remember that’s just for one of the
trapezoid shapes of the hip roof in this example there are two trapezoid shapes
in the illustration you can see this hip roof has two trapezoid shapes and two
triangle shapes so let’s look at calculating the area of a triangle the
area of a triangle regardless of the triangle shape is base times height
times 1/2 in this example the area of the triangle is 8 feet times 10 feet
times one-half equals 40 square feet the four planes of a hip roof include two
triangles and two trapezoids calculate the area of each shape and add
them all together to get the total square footage of the hip roof area
there are several different types of roofs and their area calculations let’s take a complex house roof as an
example and calculate its total square footage this complex roof has lengths of
various geometric shapes of the roof measured the main house roof is a large
gable roof looks like the front entry has a small gable roof the rear deck has
a hip roof there and there’s a gazebo roof attached to the back of the house
let’s calculate the area of this complex roof in total square footage let’s start
with the red octagon a4 which is just like a bunch of triangles stuck together
we know that the area of a triangle is base times height times 1/2 so the
octagon is 8 of those triangles added together so if the base is 5 feet and
the height is 6 the area of the octagon is 8 times base times height times 1/2
and it equals 120 square feet now let’s look at the yellow shapes the area of
the east gable a3 is the addition of 2 trapezoids we know that the area of a
trapezoid is base one plus base 2 times height times 1/2 so for this house the
east gable a3 is 16 feet 3 inches plus 10 times 5 which is height times 1/2 but
because there are two trapezoids you double that amount to get the total
square footage of the east gable roof in yellow the west gable roof is measured
by calculating the area of one of the trapezoids and then doubling it to get
the total square footage it’s the same method we used for the East gable roof
next is the big blue section a gable roof with two large rectangular Plains
we know that the area of a rectangle is base times height for this house roof we
have base times height as 10 times 60 or 600 square feet
there are two rectangular planes the total square footage of the blue main
house roof a 1 is double that 1200 square feet due to the overlap in areas
we must subtract a portion of each yellow gable from the main house roof
total so the green dashed lines indicate the areas that must be subtracted from
the main house roof a 1 here’s the breakdown of all the shapes and their
areas you when you add up all the shapes the total
roof area is 1820 square feet now convert the total square footage to
roofing squares in roofing terminology a square is 100 square feet now divide the
total area by 100 so 1820 square feet that’s the total area of the entire
house roof divided by 100 equals 18.2 squares this answer is the number of
roofing squares for the roof 18.2 so in summary we learned how to calculate the
size of a roof by measuring the total square footage of the roof and dividing
that by 100 remember the area of a square is simply base times height the
area of a rectangle is just like a square base times height the area of a
triangle is base times height times 1/2 the area of a trapezoid is base one plus
base two times the height times 1/2 and a square in roofing terms is 100 square

Comments (43)

  1. You said multiply several times for the trapezoid measurement when it's actually dividing by 2.

  2. A software package has been developed to make such measurements. But knowing how to do this manually is necessary. Knowing the basics first is necessary in any profession.

  3. Yes expanding on what Eric Brennan Said when talking about trapezoid in the beginning you said Base 1+Base 2 divided by 2 at the end you in the final summary of all the calculations it says Base 1 + Base 2 x 1/2 and at the end you say the same thing but it shows Base 1+Base 2 divided by 2. Which one is it? Can you please correct this or can someone comment or leave a video note?

  4. Nick, multiplying something by 1/2 or dividing by 2 equals the same number… Example : 100 divided by 2 = 50 or 100 x .5 (1/2) = 50… So, you can do it either way…

  5. Measuring the area of the house footprint will not work. You also need to add in your overhangs of eaves and rakes, then it will work. You could cost someone thousands of dollars by making this simple mistake. have a good day.

  6. Ben, when you show the East gable at 6:08 in the video you explain the base as 2 different lengths. Why do you show 10 foot and 16.3 and not just a 3rd line showing 26.3 length total. This looks confusing when looking at the roof design. So what your saying is that from the edge of the main roof to the end of the gable is 10ft and the triangular portion length is 16.3 feet? why would you double a length just to subtract the triangular portion. Couldn't you just measure the triangular parts of the roof and do it separately? Then subtract the triangular portion from the main portion of the house? it confuses me how you take two lengths add them together then do your base X height X 1/2. Please let me know why its done this way

  7. Why couldnt you measure the A1 and measure A3 as LxW and not subtract two triangles per gable?

  8. Very help full. Thanks for sharing your power.

  9. You make it very easy 🙂

  10. The calculation is not A1, A2 and A3 is not as complex as described. It is simply 60x10x2, 20x10x2 and 5x10x2 or 2100 total. No need to add and subtract the common triangles.

  11. when it comes to the roof measurements what is the most efficient way of measuring the length, width, and or height of each side of those shapes?

  12. Just one thing didn't mention adding wast percentage for different roofs different percentages

  13. Don we consider the roof angle when measuring roof.. 45 deg, 30 deg.. like that.

  14. very straightforward and professionally done. Bravo ! kiss

  15. You also don't mention starter shingles and roof caps so whoever uses this as a home owner to attempt to do his roof will be short.

  16. That was very helpful, Thank you

  17. There is no need for this complexity in calculating the area – it is simply
    60x10x2 = 1200
    20x10x2 = 400
    10x5x2 = 100
    6x5x0.5×8 = 120
    Total 1820
    It is hard to believe that home inspectors would need training on such a basic estimation.


  19. Di you Givin Roofing Classes?

  20. Nice video keep it up this video was crystal clear on how to learn to estimate a roof. Thank you

  21. Hi Ben, excellent job with the videos. You are a true teacher!

  22. My head is about to explode

  23. this is a great one Ben,thx for the video

  24. Good evening sir
    Thank you for demonstration & it will help me a lot you doing very your good job,keep up your demonstration & tutorial thank you,

  25. Thank you so much Ben! IT's so easy and to the point!

  26. This works in simple roofs like a shed roof home but when you have gables and eves and rakes it's tougher I use this sky measure software whe 're you pay 40 to get the aerial Square footage of a home only thing it's not always guaranteed if there's alot of trees covering the home that's the only disadvantage

  27. So the software that I'm using is Sky measure powered by core logic, so 80% of U.S. homes sold are included in property imagery, averaging 9 images per home so more than likely it could definitely save you time and money their fees vary I haven't paid but 40$ per home we've done, but it saves a ton of time in the long run they also have an app for easy login access

  28. Best roofing measure video I've seen, thanks for sharing

  29. Wtf do u mean by half

  30. Ben this video most definitely refresh my memory, I almost grab my pen and paper and started to make up my own measurements 😂😂. Thank you for making this video. Very easy. Very simple

  31. Awesome.hey what's up buddy.i have a cuestion .how many bags of ridge are on 92 feet.

  32. 6:40 that's wrong, you have to get the slope and multiply by the sloped length, not the projection

  33. This video was just what I needed! Thank you!

  34. I never knew how many bundles to buy

  35. @ 4:00 you said 10 times 8 times 2 = 40 squares. Was that an error or am I all wrong?

  36. I've measured alot of Roofs, in my day. I personally think; you made this sound, more complicated, then it really is. Your graphics, for the trapezoid, were useless. I stopped watching there.

  37. Thank you can't believe how many years have been doing this and I still forget this equation

  38. Well… I guess I won't be applying for a roofer position anytime soon… I might accidentally overcharge customers with calculation

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