a list as long as your arma list as long as (your) arm
if you say a list is as long as your arm, you mean that it is very long.
Anyway, I'd better make a start. I've got a list as long as my arm of jobs to do.
list as long as (one's) arm
A very long list of items to accomplish. I'm too busy to make it to dinner tonight—I have a list as long as my arm to finish.
a list as long as your arm
INFORMAL
COMMON If you have a list as long as your arm, you have a very long list. I've got a list of players as long as your arm but it's just a matter of whether they're available. Note: The word list can be replaced by other words that refer to things that can be written as a list. By his late 30s, he already had a rap sheet as long as your arm — 52 convictions and a total of 16 years behind bars.