Do you ever use a hip belt?

I bought a 30 liter Camelbak Commander camo hunting pack. It had a wimpy plastic frame sheet and unpadded cloth belt.

MODS.:
1. cut off belt & buy REI Ridgeline padded belt to insert behind the Camelbak lumbar pad. PERFECT FIT!
2.make an upside down U frame of three 1" aluminum strips bolted into holes melted through the pack and frame sheet, the 2 vertical stays contoured to my back.

Now I have a hunting/backcountry skiing pack with a frame that transfers the weight to my hips, not my shoulders and spine. It has seen many miles of use and everything works as designed.

"I would never use a backpack weighing more than 15 pounds without a hip belt. Plus, I feel uncomfortable if there is no sternum strap."

Agree.

> Is the medium Zero pack less volume than the exodus or about the same?

I took a few simple measurements (and photos) of both the Exodus and the Zero.

Here they are, lying next to each other:

As a reminder, the Zero is a size Medium.

I measured the height and width of them lying flat. The cuben tended to crinkle when it wasn't stretched and held, so the Zero appears slightly smaller in the photos than it truly is. It also introduces a little more uncertainty in the measurements of the Zero.

The measurements were roughly:

Exodus: 18" x 35.5" (w x h)
Zero: 17" x 32" (w x h)

If we assume these look like flattened cylinders, then the radii of the cylinder (and the opening) and the volume of the cylinders are:

Exodus: radius = 5.73", volume = 3,660 in^3
Zero: radius = 5.41", volume = 2,940 in^3

These volume numbers are, of course, overestimating volume; in reality, these packs will not take the shape of perfect cylinders, and perfect cylinders maximize the volume per unit surface area (as compared all cross-sectional shapes other than circular). This also calculates the volume to the top of the collar, which is not all usable volume.

Manufacturer specified volumes are:

Exodus: volume = 2,400 in^3 (main pack) + 500 in^3 (collar)
Zero: volume = 2,200 in^3

Zpacks didn't specify how full the collar was on their measurements.

If I subtract three inches from the height of my measurements, to allow closure of the collar, the new volumes are:

Exodus: volume = 3,350 in^3
Zero: volume = 2,670 in^3

The ratio of the Zero's volume above to the Exodus' volume is 80%. That seems like a reasonable place to stop–the Zero (medium) probably has a volume of around 80% that of the Exodus. Caveated by, of course, the fact that these were based on rough measurements and several simplifying assumptions.

Hope this helps.

Thanks Adam! That definitely helps. I'll be looking into swapping out my pack for zpacks in the future.