Measure the length of a rectangular building, like a backyard storage building, with the measuring tape. Have your assistant hold the end of the tape at one corner of the storage building while you walk to the opposite corner on the longest side. Keep the tape as close to the surface of the building as possible, for the most accurate measurement. Read the measurement from the tape and record it, using pencil and paper.
How to Size by the Square Foot
Many things, like houses and buildings, are described in terms of square feet. When someone says a building has three acres of floor space, you might wonder how they sized the building and determined the number of square feet. You know that there are 43,560 square feet in an acre, but you might also wonder how they determined that there were three acres130,680 square feetunder the roof. The answer comes from some measurements and a little bit of practical math and works as well for a front yard as it does for a building.
Things You'll Need
 Measuring tape
 Assistant
 Pencil
 Paper
 Calculator
Instructions


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Have your assistant come to you and stand in your place and again, have him hold the tape at the corner of the storage building. Walk to the opposite corner on the short side, keeping the tape near the surface of the building. Read and record the measurement from the tape.


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Use your calculator to multiply the two measurements together. If the long side of the storage building was 12 feet long and the short side of the storage building was 8 feet long, multiply 12 by 8: 12 x 8 = 96. The answer, 96, is the size of the building in square feet.

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Tips & Warnings
 If the shape of the building is a group of rectangles, you must "break the building up"look at each of the rectangles as if each were a separate building. You measure each as a separate rectangle, calculate the size of each rectangle in square feet, then add up the results of the individual calculations: 10 square feet + 15 square feet + 30 square feet = 55 square feet total.