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.
I don't know the exact number, but by a rough estimate I think it's about 50 people.
Short for 目の子算用, calculation performed by visually estimating quantities instead of using an abacus or other precise method.