measuring box, (kokuji)
枡 centers on a wooden container used for measuring, specifically a traditional square measuring box. As a kokuji, it was created in Japan for this specific purpose.
枡 is a kokuji (Japanese-made kanji) combining 木 (wood) with 升 (a measuring unit or box), reflecting a wooden measuring box.
The left side 木 is wood, and the right side 升 looks like a box with a handle. Picture a wooden box used for measuring rice or sake.
For ます, imagine a wooden measuring box filled with a mass of rice: mass -> ます, and the box is made of wood.
—