目めの子こ算ざん

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.

• 買かい物もののときはいつも目めの子こ算ざんで合ごう計けいを出だす。

  When shopping, I always figure out the total with a rough mental estimate.

• 正せい確かくな数すう字じはわからないけど、目めの子こ算ざんでだいたい50人にんくらいだと思おもう。

  I don't know the exact number, but by a rough estimate I think it's about 50 people.