noun
internal volume; capacity
Technical term used in engineering, packaging, and specifications to denote the volume inside a container or space.
この容器の内容積は500ミリリットルです。
The internal volume of this container is 500 milliliters.
容積 is a more general term for volume or capacity, while 内容積 specifically refers to the internal volume of a container or space.
Compound of 内容 (ないよう, 'contents') and 積 (せき, 'volume'). The exact historical derivation is uncertain, but the term is a straightforward technical compound.