Will a small laptop mesenger bag fit a Dell M1330?

My macbook, 13'', fits in my small messenger with some room to spare.

I usually only carry my laptop, keys, wallet and a few other random items (ball of yarn, lunch, sweater).

If you're looking to carry your laptop in a sleeve and a ton of other items I would go with the medium. I'm probably going to go up a size soon so I can haul around more things when I need to.

Hope this helps!