量 (liàng) is a noun meaning 'quantity, amount, capacity' — it's the general word for how much of something there is. Its sibling 数量 (shù liàng) is more specific, referring to a countable number or sum; 容量 (róng liàng) is 'capacity' in the sense of how much a container holds; and 音量 (yīn liàng) is 'volume' of sound. The verb 量 (liáng, HSK4) is a different word with a different tone and meaning.