From Longman Dictionary of Contemporary Englishas long as your armas long as your arminformalLONG a list or written document that is as long as your arm is very long I’ve got a list of things to do as long as your arm. → arm
Examples from the Corpus
as long as your arm• Instead of hiring child care I traded it with other parents: I had a list as long as my arm.• Mr Linley stuck out a microphone as long as his arm, right up to those ragged jaws.• My record's as long as my arm - even longer. 