Oi everyone,
why are we so really really bad at efficiency when it comes to hull size vs. cargo. Take any T1, T2 hauler, Freighter or JF. Go to their info window, click on the image and see their longest axis in metres. Now make some educated guess (or measure dimensions on screen) about Y and Z axis. Go for any amount lower than the average length of each axis, depending on its shape, just to be within reason. It gives you (X,Y,Z)  a rough estimate of their volume in m3. Another option is to just go to the ATTRIBUTES tab on the info window and look for unpackaged Volume there. You will find that often enough unrepacked size on the Attributes page will make no sense if you look at the image mentioned before.
Take the Ishtar as a random example: 115,000m3 unpackaged. Longest axis: 239m. Open the image and look at the model. To make it easy, completely ignore the lower part. Shorten the 239m to let’s say 180m or 75% for calculations. Estimate the upper part of the Ishtar for Y axis at 60m and now turn it around to see its face. 180m x 60m = 10,800m2. Which leaves for an average of under 11m of the Zaxis (face view, upper part) to stay within 115,000m3. And that’s ignoring the lower part.
Okay, Epithal, another one. 553m long. Lower average for both Y and Z axis (kind of round) would be around 0.08 of that or roughly 44m. Y * Z = (44m/2)^2 * 3.14159 so roughly 1537m2. Makes for a Volume of 850,000 instead of the 250,000m3 on the info page.
Seems like the larger the ships get the more serious this gets: Phoenix, 16,250,000m3 unpackaged according to Attribute tab. 3756m longest axis and fairly rectangular. With X = 3756m it leaves for (Y,Z) for 4393m2 to be somewhere around the size it shall have. Now 4393m2 is below 67m x 67m, meaning Y and Zaxis would be an average of 67 times shorter than Xaxis. Look at the image. 67 times shorter is the girth of a broom compared to its length. Not a broom!
While this is not always the case (esp. on frigates number seem to make more sense), your ships axis length will determine things like bumping and size has important implications on Signature radius (which becomes important when someone locks you or shoots you), so that’s something to keep in mind. Often enough you’ll find the actual Volume in m3 should be 10 times larger than in the Attribute page.
So really, wtf went wrong there? Does it have to do with something no one wants to touch due to Signature radius or such? Whatever it is, please be nice to math.
Which leads me to haulers, T1, T2 and Freighters. I find it already hard to conceive how a ship that big that doesn’t bring any specialized Power system for fitting bulky tank, guns (and sometimes not even MWD) or anything alike can be so large (even just the “official” size according to Attribute tab) and have such a little actual space for cargo. The actual dimensions are even larger.
Let’s make a comparions  Probe vs. Wreathe & Mammoth:
Minmatar T1 Frigate vs. Minmatar T1 Hauler.
A. Cargohold:
Probe: 400m3 base  1372.9m3 with maxed cargohold extenders and rigs.
Wreathe: 2900m3 base  3625m3 base max skills  20226.4m3 with max skills & extenders/rigs.
Mammoth:  5500m3 base  6875m3 max skills  38360,5m3 with max skills & extenders/rigs.
B. HullSize:
Probe: 19,500m3 unpackaged, realistic, maybe even smaller.
Wreathe: 225,000m3 unpackaged, realistically easily above 1,000,000m3. (>400%)
Mammoth: 255,000m3 unpackaged, realistically easily above 2,000,000m3 (>800%)
C. Comparison:
Let’s compare the Volume of each ship with its max cargohold  both are in m3 so we just need simple math to get a hold of it. I will calculate in the form of “Cargohold” / (“HullVolume” / 100) to get X, which is the % of m3 in Cargohold of the overall m3 of said ship.

Probe:
X = 2,05% for unfitted; 7,04% for maxed cargo.
(official and realistic size are close enough to not make any meaningful difference here). 
Wreathe
“official”: X = 1,61% for max skills&unfitted; 8,98% for maxed cargo.
“realistic size”: 0,36% for max skills&unfitted; 2,02% for maxed cargo. 
Mammoth:
“official”: X = 2,69% max skills,unfitted; 15,04% for maxed cargo.
“realistic size”: 0,34% for max skills&unfitted; 1,91% for maxed cargo.
It means if we are talking realistic sizes (actual metrics and not that number on the Attributes tab), we end up with an unfitted Probe LVL1 having a higher cargo efficiency than a fully fitted and max skilled T1 hauler. It also means that on a max skilled and maxed out cargofitted T1 Hauler you have 2% of the overall Volume for cargo  at best. That’s like declaring shopping a success, because two bottles of milk.
How about make them haulers smaller in size? CCP? Or somehow fiddle with Sig radius, because in all of that it makes the least sense to me. Or just any explanation why it has to be like that and why everything else is just crazy talk. Thanks.