long as your arm
as long as (one's) arm
Very long. Typically used in the phrase "a list as long as (one's) arm." I'm too busy to make it to dinner tonight—I have a list as long as my arm to finish.
long as your armINFORMAL
If something such as a list is as long as your arm, it is very long. The phone's been buzzing non-stop. I've a list of messages as long as my arm.