DIY Home Improvement Measurements: Square Feet
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DIY Home Improvement Measurements: Square Feet

by TimJones on March 23, 2010

What is a square foot measurement?  Well, even though it may sound a little complicated, square feet is one of the easiest measurements, other than lineal feet or distance.  Square feet is a width multiplied by a length to find the area of a space or object.  So, if a room measures 10 feet by 12 feet, the floor area (assuming it’s an open floor) would equal 120 square feet (10′ x 12′ = 120 sq. ft.).

Common Square Feet Materials

  • Tile
  • Countertops
  • Flooring (except carpeting)
  • Drywall
  • Plywood
  • Unit cost calculations (this is a more complicated subject for another post, but just be aware that this is the common measurement base for unit cost calculations)


Sometimes, with square feet calculations, you need to make a few conversions to get an accurate measurement.

  • Tile: Sometimes, you need to convert a square foot measurement to the number of tiles or vice-versa.  Tile generally comes packaged in “X number of tiles” sets at your local home improvement store.  Therefore, you need to be sure you’re measurements all follow the same base; either square feet or number of tiles.  So, you generally need to determine how many square feet each tile covers to buy the proper quantity.  To do this, remember that a square foot is just one foot width by one foot length.  Now, just convert each tile size (in inches) to a foot measurement.  For example, a 12″ by 12″ tile is exactly 1 square foot.  An 8″ tile becomes 8/12 (or 2/3′ or .666667′) by 8/12′ = .44 square feet coverage per tile.  Now, multiply that square foot coverage by the number of tiles per box.  Now, divide the total square feet you need for the project by the number of square feet covered by box and that will tell you how many boxes of tile to buy.  Please note: This does not include the grout or waste!  Grout spacing varies, so be sure to add that to your measurements.  Therefore, assuming you use a 1/4″ grout line (pretty big, BTW), then you need to add 1/8″ to each tile dimension.  This really complicates matters and you’re better off looking at how much each case covers.  Almost all home stores make this calculation for you.
  • Drywall and Plywood: Drywall and plywood comes in 4′ x 8′ sheets, so each sheet covers 32 square feet.  Therefore, anytime you’re measuring for drywall or plywood (height of the wall by length of the wall, less openings), you need to divide your total square feet measurement by 32 to get the number of sheets you need for the project.

Material Waste Factors

I’ll probably remind you about waste factors throughout this series, but for all material ordering and quantifying, you need to include a waste factor.  Essentially, this means you need a order or buy a little more material than just the strict square foot coverage you calculated in your measurements.  This covers cuts around openings, door frames, etc. as well as any errors you make in installation.

You can get very detailed information on what waste factors to use with which materials just by searching for it on the internet.  I don’t, nor do I expect the average homeowner to calculate waste factor’s for each material they’re using on a project and getting every material down to a very finite quantity.  Let’s leave that kind of detail to the professionals.

Generally, I’ve found 15% to serve me very well for my home improvement projects.  If you’re trying to stick to a very tight budget, you may work with a 10% waste factor, but you need to efficiently use your materials in this case or you won’t have enough to complete the project.

So, once you’ve calculated the square feet you need to cover, multiply that number by .15 to get the square footage measurement you’ll use for all material ordering.

Tomorrow, we’ll talk about cubic yards and when you need to calculate this quantity.

Related posts:

  1. DIY Home Improvement Measurements
  2. How To Measure Square Yards
  3. How To Measure Cubic Yards

{ 1 comment… read it below or add one }

DON August 26, 2011 at 5:57 pm

I am making a speaker box for car audio. I need to know the inch for a 3.00cuft box/

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