How many cans fit in there?
I have a collection of backpacks, of varying sizes. They all have “official” sizes, measured in liters. The standard way to compare sizes of backpacks when shopping online, is to compare the liter size rating.
I feel that a more practical, and repeatable, measure of capacity is the “cans of beer” test. I actually use cans of diet coke, since I don’t drink beer, but let’s assume they’re equivalent.
In the “liters” column we have the official size rating of the bag. The “# of 12oz cans” column indicates how many cans I was able to reasonably stuff into the bag.
There are some interesting observations we can make here.
There are several bags all rated at “26L” (“25L” for the ghost) that range from 38 cans up to 47 cans. That’s nearly 24% difference in actual size, but with the same rating.
The difference between the actual largest “26L” bag (the Smart Alec) and the “30L” bag (the Medio) is only 1 can. And actually, if you don’t include the 6 cans stuffed into the outer pocket of the Medio, it has less capacity than the Smart Alec, despite being rated as larger.
Another dramatic variance, is the difference between the Fitzroy and the Especial Tres, both rated at “40L”. The Tres has 28% more capacity.
I want to point out that I really don’t think any of these brands are lying, or even trying to mislead. I expect that the biggest variances are simply due to being more or less conservative in their ratings. For instance, I’m sure that the 40L rating for the Especial Tres is meant to be “normal” capacity, i.e. before expanding the expansion sections and unrolling the rolltop as far as possible. There’s probably even a fear of advertising too large a number and scaring potential buyers.
Another source of variance is that stuffing a bag with cans changes the shape, and therefore, the capacity, of the bag. The rated capacities are likely in “as designed” shape. For instance, after stuffing the GR1 with cans, it’s not exactly the near rectangle of it’s original design.
As I said at the beginning, I think “cans of beer” (or “cans of diet coke”) is a more practical & repeatable measure of bag capacity. I think it would be awesome if bag manufacturers would provide this number as one of their specs. It’s a measurement that just about anybody can confirm or deny with a simple test, without filling a bag with sand or water or something.