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.
See also: arm, long

long as your arm

INFORMAL
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.
See also: arm, long