Refrigerators are sold with their internal capacity volume listed as cubic feet, regardless of what racks, shelving and unusual internal configurations take up space inside. For comparative purposes, you can calculate this number for your own refrigerator with a tape measure and three quick measurements. Calculate the volume of the freezer and refrigerator compartments separately. Since the interior of a refrigerator is just a box, use the formula for the volume of a box: length x width x height.
Things You'll Need
 Measuring tape

Measure the interior length, width and height in feet of the refrigerator inside the cooling chamber. Only measure parts of the refrigerator inside when it the door is closed.

Multiply the length times the width times the height. For instance, if the inside measured 2 feet by 3 feet by 2 feet, the volume would be: 2 x 3 x 2 = 12 cubic feet.

Find the average usable space inside your refrigerator by multiplying the total cubic feet by 65 percent if you have a sidebyside, or 78 percent if the freezer is located on the top or bottom. For the example, if a 12cubicfoot refrigerator is a sidebyside, calculate: 12 x 65 percent = 7.8 cubic feet. If the freezer on top, calculate: 12 x 78 percent = 9.36 cubic feet.
References
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