how long is a piece of string?
idiomPart oflong
how long is a piece of string? — idiom
1. Used to say that there is no definite answer to a question.
1.idiom
Definition
Used to say that there is no definite answer to a question.
Example
When asked how long the project would take, he replied, 'How long is a piece of string?'
How long is a piece of string? It depends on many factors.