Bag Sizes
 

So Ive been searching a new bag. My question is what can I fit in different sizes. I have no idea what size my bag is now but its really more that I need. I carry pants, dress shirt, undershirt, maybe a soda and can of soup and maybe a book or my laptop.

Im cuurently looking 20L anyone use this size carry the same?

Depends on the size of the book/laptop. I use a pair of Ortlieb Front Rollers that are listed at 25L combined. I carry leftovers in Tupperware, clothes for the day, and a small laptop. Those panniers are a good fit for that load and leave room for a few additional items as needed. The addition of a pair of shoes brings me nearer the capacity limit.

15.4in laptop, though my books can get pretty thick, like Harry potter hardcover size.

If that fills up 25l I'll probably look at at least 30 for just in case moments