rough estimate; mental arithmetic
Refers to a quick, approximate calculation done in one's head, often by eye or intuition rather than precise measurement. Common in informal contexts.
When shopping, I always figure out the total with a rough mental estimate.
正確な数字はわからないけど、目の子算でだいたい50人くらいだと思う。
I don't know the exact number, but by a rough estimate I think it's about 50 people.
概算 is a general term for approximate calculation, often used in formal or business contexts. 目の子算 is more colloquial and implies a quick, by-eye judgment.
Short for 目の子算用, calculation performed by visually estimating quantities instead of using an abacus or other precise method.