Capacity refers to the amount of space inside a container that can be filled, whereas volume is the amount of space that an object occupies. A hollow object can have both capacity and volume, whereas a solid object has volume only.
Both capacity and volume are calculated by multiplying length, width and height — either internally or externally. Since the difference can be negligible, volume and capacity are often used as synonyms.
The capacity of an irregularly shaped container can be found by filling it with a liquid then transferring that liquid to another container of which the capacity is known, such as a measuring jug. Finding the volume of an irregularly shaped object requires breaking it down into component parts, such as polygons, to be measured separately.