noun
quantity contained; number per unit
Used in packaging, shipping, and inventory contexts to indicate how many items are inside a carton, packet, or container.
この箱の入り数は24個です。
The quantity per carton is 24 pieces.
パッケージの入り数を確認してください。
Please check the number contained in the package.
数量 is a general term for quantity or amount, while 入り数 specifically refers to the number of items inside a container or package.
Compound of 入り (iri, 'entering' or 'contained') and 数 (sū, 'number'). The exact historical derivation is uncertain, but the word is a straightforward combination of these elements.