Is the Zeitgeist volume underestimated??

[Surrealle]

Okay so I'm confused here.. The Zeitgeist dimensions are listed as

12.8" (h) x 9.8" (w) x 4.7" (d)

and it's rated at 6.7L, whereas the Co-pilot is

11.8" (w) x 10" (h) x 4.9" (d)

and it's 10L with more pockets/dividers that typically eat up space. I know measuring volume isn't an exact science but isn't that a bigger difference than one would expect for such similar dimensions?

[Cristina]

I’m going to flag Darcy for this one. I agree those specs are surprising.

[Surrealle]

I’m going to flag Darcy for this one. I agree those specs are surprising.

Thanks! I’m very curious to know the reason, as the main thing keeping me from ordering one is that the volume is too small.

Edit: Hmm, it’s hard to tell from the pics but I just realized it looks like it’s tapering to the top, which I’m guessing could account for the difference. Sorry for the possible false alarm! (I’ll delete this if that ends up being the case.)

[sturbridge]

I had to go pull my co pilot out of the closet and compare it to my ZG. It looks /very/ similar in size

[bchaplin]

If I was willing to sacrifice the dried beans I stashed away from mid-2020, I could answer this question in a scientific way. Does anyone remember what the company uses to determine the volumes?

[ThomGault]

Does anyone remember what the company uses to determine the volumes?

IIRC, small styrofoam balls.

[Darcy]

As we’ve talked about elsewhere (but I couldn't find it when I searched, I'm no moriond that's for sure!), when we measure the volume of a bag, we use a modified ASTM standard method: we fill the bag with hard plastic balls to a point that it is reasonably full, then we measure the weight of the balls (having previously calculated the weight to volume ratio for the balls). This gives us and you a relatively standardized view of how much stuff you can put inside the bag.

When the bag is in this state of being reasonably full of the hard plastic balls, we use a large caliper to measure the bag’s extreme height, width and length (we ignore protruding handles, just measuring the bag and any exterior pockets). Imagine, if you will, that we are going to build ourselves a rigid box into which we can easily slide the now filled bag: that’s pretty much what those three dimensions are giving you. If a bag is relatively rectangular, it’s going to fill that rigid box more completely than if it’s relatively curvilinear: think of an Aeronaut (which is square-ish and designed to fill the maximum allowed carry-on space), compared to a Synapse (which has many curved surfaces).

Or, for the sake of illustration, think of a VW Beetle vs a Honda Element:


You can see that the box around the Element is much more filled-in by the vehicle than the box around the Beetle, yet they are pretty much the same size boxes! If we actually built boxes for these two cars and wanted to ship them to you, you can see we’d use a lot more packing peanuts to fill in around the Beetle than we would around the Element.

This fun video further illustrates how much volume is impacted by curved surfaces; it takes the extreme case of comparing a sphere to a cube (both with the same gross three dimensions of 5cm x 5cm x 5cm):
https://www.youtube.com/watch?v=QNpmxGpey_0

[epeterson]

when we measure the volume of a bag, we use a modified ASTM standard method: we fill the bag with hard plastic balls to a point that it is reasonably full, then we measure the weight of the balls (having previously calculated the weight to volume ratio for the balls).

This would make a fun little Instagram video, just saying...

[bchaplin]

Surrealle : I tried out my Zeitgeist on my commute today for the first time. It was so tiny compared to the Paragon that it almost seemed like a toy! The Zeitgeist basically fit everything I needed, but just that, minus the spare umbrella or sweater I usually carry. Contents were: HLT-1, and Small and Mini Ghost Whale pouches, topped by an Everyday Cubelet, square cubelet, and 12oz Zojirushi coffee mug. Some flat things such as masks and index cards were slotted in. It was definitely full, with maybe an inch of headroom, though not bursting at the seams. I could have added a Kindle or iPad if I'd wanted to, in the device pocket.

So when I got home today I moved all the contents into a Co-Pilot. It's a little difficult to compare the two because the CP is segmented, but there was space left over once I moved everything into it. One front pocket was completely empty and the other only half-filled, and more items could have gone into the back as well. So that's consistent with the difference in the stated volumes between the Zeitgeist and the Co-Pilot.

I like the Zeitgeist a lot! But it won't be my everyday carry; more for times when I want a backpack that is very small and light. And cute.

Hope that helps!

Two pics of the Zeitgeist packed as described above.

Note that it almost looks pink in the photo due to the full sun; however, it's not that way in real-life. This shows that the Everyday Cubelet, square cubelet, and coffee mug take up the top half of the bag. Underneath those: the HLT-1 and the two pouches.



And, to show that it was just about filled to capacity:

[moriond]

As we’ve talked about elsewhere (but I couldn't find it when I searched, I'm no moriond that's for sure!), when we measure the volume of a bag, we use a modified ASTM standard method: we fill the bag with hard plastic balls to a point that it is reasonably full, then we measure the weight of the balls (having previously calculated the weight to volume ratio for the balls). This gives us and you a relatively standardized view of how much stuff you can put inside the bag.


When the bag is in this state of being reasonably full of the hard plastic balls, we use a large caliper to measure the bag’s extreme height, width and length (we ignore protruding handles, just measuring the bag and any exterior pockets). Imagine, if you will, that we are going to build ourselves a rigid box into which we can easily slide the now filled bag: that’s pretty much what those three dimensions are giving you. If a bag is relatively rectangular, it’s going to fill that rigid box more completely than if it’s relatively curvilinear: think of an Aeronaut (which is square-ish and designed to fill the maximum allowed carry-on space), compared to a Synapse (which has many curved surfaces).

…

<snip> (so I’ve left out all the good stuff in pictures)

Darcy
The most recent time that you went through the exercise of describing how you measure these dimensions was in your post (#80 dated 05-04-2021) in the thread about Le Grande Derrière that Walker started in 02-13-2021. Here’s a quote:

I'll add this to the FAQ, but real quick here:

We measured the LGD using the same methodology we use to measure all our bags: we fill them with .75” / 20mm hard plastic spheres and pack them reasonably tight. We then measure the tallest, thickest and widest dimensions using a large caliper. The thickest (deepest) dimension of the LGD is just over 6".

The operative part of that explanation was the part about measuring the tallest, thickest and widest dimensions. This is how you get the tie-in to your fun pictures, and why people were asking whether the LGD was really that thick.

HTH

moriond

[Hanaper]

Note that it almost looks pink in the photo due to the full sun; however, it's not that way in real-life. [...]

A note to the company that I could be quite interested if they ever did match the shade of deep rose that was caught in your images.