ㄖㄣˊrénㄅㄨˋㄎㄜˇㄇㄠˋmàoㄒㄧㄤˋxiàngㄏㄞˇhǎiㄕㄨㄟˇshuǐㄅㄨˋㄎㄜˇㄉㄡˇdǒuㄌㄧㄤˊliáng

  1. 諺語)​不能外貌判斷好壞高低·無名氏尉遲·》:「(正末)​軍師無名小將何足道哉(房玄齡)​老將古語人不可貌相,海水不可斗量。」拍案驚奇·○》:正是人不可貌相,海水不可斗量只是女婿不在。」

you can't judge a person by appearance, just as you can't measure the sea with a pint pot (idiom)​