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While you may not often think about the capacity of your freezer, in some cases, the measurement comes in handy. For instance, if you are buying a large quantity of prepackaged meet or storing a catch of fish for a friend, calculating the true number of cubic feet of storage space lets you know if you have enough room to take on the storage task. When it's time to buy a new chest freezer, knowing the capacity of the existing freezer ensures you'll buy one with enough space for your needs -- exterior size alone is not an indication of interior capacity, nor is the manufacturer's claim necessarily accurate.
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Remove all the items from within the freezer, or at least push items to the side while taking each measurement.
Measure the depth of the freezer from the bottom to the highest point it can be filled without obstructing the lid. Jot the number down on scrap paper, using feet as a measurement. For instance, 2 feet 6 inches is written as 2.5 feet. Every 3 inches equals 0.25 additional feet -- 9 inches equals 0.75 feet.
Measure the interior width of the freezer from one inner wall across to the other. Jot that number down as well, in feet.
Measure the interior of the freezer from front inside wall to back inside wall. Jot down this measurement in feet.
Multiply the three numbers together to determine capacity of the freezer in cubic feet.
As a real-world example, a freezer with an interior measuring 16 inches (1.33 feet) from front to back, 35.5 inches long (2.97 feet) and 27 inches (2.25 feet) deep is nominally 8.89 cubic feet. Convert inches to feet by dividing the inches by 12. A compressor bumpout 10 inches high (0.83 feet) by 11 inches (0.917 feet) deep takes up 0.76 cubic feet, so the actual space of the freezer is 8.13 cubic feet. Note that some freezer manufacturers do not subtract space eaten up by bumpouts, so the actual capacity may be less than what they claim.
If some of the freezer space inside is taken up by obstructions so the interior is not completely the same throughout, measure the object's height, width and depth and multiply them together, in feet. Subtract this amount from the total cubic feet of the freezer storage compartment.
When you size a new chest freezer, estimate 1.5 cubic feet of storage space for food per person in the home. One cubic foot of freezer space holds approximately 35 pounds of food, according to the University of Illinois Cooperative Extension Service. These numbers may vary if you freeze a lot of food or buy bulk frozen goods.