壁かべ越ごし推すい量りょう

noun

guesstimating; rough estimation through a wall

Literally 'estimation through a wall'; used for making a rough guess based on limited or indirect information, often in a humorous or self-deprecating way.

• 隣となりの部屋へやの話はなし声ごえから、壁かべ越ごし推すい量りょうで会かい議ぎの内ない容ようを想そう像ぞうした。

  I imagined the meeting content by guesstimating through the wall from the voices next door.

• 彼かれの給きゅう料りょうを壁かべ越ごし推すい量りょうで当あててみたけど、外はずれた。

  I tried to guess his salary by rough estimation, but I was wrong.