To reduce space requirements for trash removal, compacting garbage removes any loose space. At times this can considerably reduce the volume of trash collected. The amount this volume is reduced by is called the compaction ratio. For example, a compaction ratio of four to one, sometime written as "four" with the "to one" understood, tells you that four times the volume of compacted waste can be placed in the same storage space occupied by the noncompacted waste. This information helps estimate future trash storage needs or measures the efficiency of your compactor.

Measure the volume of the loose trash or garbage. If you have filled up a 200 gallon trash can, then that is your volume. If you have a box of trash that measures 2-by-2-by-4 feet, the volume is calculated by multiplying those dimensions together. In the case, the box has a volume of 16 cubic feet.

Compact the loose trash using a trash compactor, such as a household model or one built into a garbage truck.

Measure the volume of the compacted trash using the same method as described in Step 1.

Divide the volume of the loose trash by the volume of the compacted trash to achieve the compaction ratio. As an example, 16 cubic feet of loose trash compacted into a 4 cubic feet volume would have a ratio of four, or four to one. A 200 gallon container filled with loose trash compacted to 50 gallon would also have a four to one compaction ratio.