目めの子こ勘かん定じょう

expression, noun

rough estimate; mental arithmetic

A quick, approximate calculation done in one's head, often by visual inspection or intuition rather than precise measurement. The phrase 目の子算 is a synonymous variant.

See also: 目の子算

• 彼かれは目めの子こ勘かん定じょうで必ひつ要ような材ざい料りょうの量りょうをざっと見み積つもった。

  He roughly estimated the amount of materials needed by mental arithmetic.

• 正せい確かくな数すう字じはわからないけど、目めの子こ勘かん定じょうでだいたい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.