Below is a table comparing the relative size of the various back-worn containers I've encountered.

Container	Length	Width	Height	Weight	Volume	Boxes
rune-covered backpack	30*	20	10	1000	6000	97
kanton's superbag	21*	15	7	1500	2205	36
beyond the barrier pack	18	13	9	1500	2106	34
hitman's backpack	18	13	8	1500	1872	29
su helmas backpack	22*	17	5	1000	1870	29?
beta backpack	23*	15	5	1000	1725	27
kanton's pack	17	11	6	1200	1122	19
crafted backpack (heavy)	14	10	7	1280	980	16
crafted backpack (fine)	18	10	5	1070	900	13
storebough backpack	15	10	5	1000	750	13

* Weapons that are 19 spans in length (i.e. most quaterstaff templates) will fit in these containers.
? The number of boxes a Su Helmas pack holds is unconfirmed.

For embiggening information: https://elanthipedia.play.net/Embiggening