Liters are a unit in the metric system used to express volume, particularly with liquids. To calculate the capacity of a container in liters, you need to know the length, width and depth of the container. For example, calculating liters can be useful if you are trying to determine how large of an aquarium you need for your fish.

Measure the length, width and depth of the container holding the liquid, in meters. For example, an aquarium might measure 1 meter long, 0.5 meters high and 0.7 meters deep.

Multiply the length times the width times the depth of the container to calculate the volume of the container in cubic meters. In this example, you would multiply 1 by 0.7 by 0.5 to find that the container has a volume of 0.35 cubic meters.

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There are 1,000 liters in a cubic meter, so you need to multiply the number of cubic meters by 1,000 to convert cubic meters to liters. Finishing this example, you would multiply 0.35 by 1,000 to find that the volume of the aquarium would be 350 liters.