expression, noun
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.
買い物のときはいつも目の子算で合計を出す。
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
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.
Literally 'eye-child calculation', suggesting a rough count done as if by a child's eye, without precise tools. The exact origin is uncertain, but it has been used since the Edo period for quick, approximate reckoning.