( BrE , informal ) used to say that there is no definite answer to a question :
'How long will it take?' 'How long's a piece of string?'
( BrE , informal ) used to say that there is no definite answer to a question :
'How long will it take?' 'How long's a piece of string?'
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005