To know something inside out is to know it thoroughly in every detail. Know something inside out after twenty years.
To know something inside out claims depth rather than breadth. Anybody who can know something inside out can also explain it simply, which is the real test.
1phraseknow something inside outTo know a subject thoroughly in every detail.
“By fifteen he seemed to know something inside out about every engine made.”
know something inside out is a phrase.
Practised in Idioms