OK, here's the poop on bale sizes:

"Small squares" has different meanings in different areas of the country.

In the midwest and east, the term "small squares" means 14x18x36" bales, about 50lbs, 70lbs maximum if you really crank the pressure up. These bales have two strings or two wires holding them together.

Then there are 16x18x36 to 40" bales.  These run a tad heavier, and in dense alfalfa, might get as heavy as 110 to 120lbs, but normally run 80 to 100 lbs. These also have two strings.

Then there are "three string" bales. These vary in size -- the older "three string" balers were 16x23x48", and could be anywhere from 110lbs up to 180lbs per bale. After enough people noticed that horsewomen just couldn't pick up a 140lb bale, hay producers started "chambering" these three-string balers down to 15.5x23 inches, and making them only about 44" long. Now we start seeing about 90 to 110 lbs in grass/grass-mix hay, still up over 110lbs in alfalfa. The problem was, when you got a really dry crop (say 10% moisture or less in the bale), getting the bale down to 100lbs for the retail market meant that the bale was mushy.

Recently, the manufactures have changed the chamber size to 15x22, which gets the weight of the bale down around 110lbs, up around 140lbs max in leafy alfalfa. Producers are still getting complaints from the horsey girls, so we see producers continuing to chamber these balers down -- to 14.5", and now the bale weight is definately 100lbs and less for a nice, hard brick-like bale. This is where I see the three-string bales finally settling for a long time -- about 14.5"x22"x44", and very close to 100lbs with a very firm bale. Mushy bales mean little or nothing to the horsey girls, but they mean everything to the truckers who have to haul them. Mushy bales mean dumped loads, and dumped loads mean truckers who are boiling mad.

The trouble with all these three-string bales is that the women east of the Rockies are wimps compared to western women. When I've taken some very high-quality hay to the Front Range in Colorado, all the retail stores tell me "That's better hay than we've ever seen -- it's utterly perfect hay, but I can't ever sell it." And the reason is that no woman east of the Rockies will pick up a 100lb bale, period, thanks for playing. Which leads me to believe that women from the intermountain west could win arm wrestling contests with midwest gals. I see Nevada women toss around 100 lbs bales all the time, no problem, no complaints. At about 140lbs, tho, I don't think that too many women who aren't from East Germany could toss the three-string bales around.

In "big square bales" there are three sizes -- 3x3 (about 1000 lbs of alfalfa), 3x4 (about 1,500 lbs), and 4x4 (about 2,000lbs), all about 8' long. The various manufactures all claim that one particular bale size or another is "perfect" for truckers. Frankly, the opinion of the trucker is last on the list of people to be consulted when buying a large baler. Any of the large balers, properly operated, will make a truck reach 80,000 lbs of loading. The height differences are not an issue unless the trucker is used to running freight instead of hay.