How to Calculate Square Footage

Knowing how to calculate square footage will come in handy when it comes time to estimate materials for that next do-it-yourself job. You'll save time, money and extra trips to the hardware store if you can accurately estimate your materials the first time.

How To Calculate Square Footage Accurately
By definition, measuring square footage requires areas that are square or rectangular. The calculation used is to measure width times length to determine the area (W x L = A). For a rectangular room of 12 by 18 feet, the square footage would be 216, since 12 x 18 = 216. Here are some tips to help with your square footage measurements:

  • Measure twice, cut once. Although it seems straightforward to measure the area of a room or garden, you'll be well served by measuring each length twice. Even the pros have been known to make a mistake or two.
  • Keep it simple squares (KISS). Trying to measure the square footage of a complicated area? Breaking the shape down into a series of squares or rectangles will make the job easier. These simple shapes can be quickly calculated and their areas added up to find a total.
  • Angles are no problem. If the shape you're measuring contains angles, break the area down into a rectangle where the angled line connects opposite corners of the rectangle. Find the area of that rectangle, and then divide the area by 2.
  • Your happy home. If you're trying to calculate the square footage of your house, use the exterior dimensions. Most appraisers and tax assessors use the method, then subtract for garages and stairwells. Your basement will count only if it's open to the outside and is finished.
  • Fudge factor. If you're buying material (gravel, wood, flooring, etc.) based on your square footage calculations, don't forget to add 10 percent to your total. This extra will help to cover waste due to cutting, loss or errors in your calculations.
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