To figure out the number of liters needed to full a container (such as a tank), divide the volume of the container, in cubic centimeters, by 1,000. One liter of water equals 1,000 cubic centimeters.
To find the volume of a tank, first find its length, width and height in centimeters. Then multiply the three digits together. The result is the volume in cubic centimeters. For example, a tank that is 50 centimeters in length, width and height has a volume of 50 x 50 x 50 or 125,000 cubic centimeters. Divide that by 1,000 to find the number of liters needed. The result is 125 liters.