Here's the problem: 28mm isn't a scale so much as a general height that sculptors use as a reference.
So what is a scale? A fair definition that I found was "the proportion that a representation of an object bears to the object itself: a model on a scale of one inch to one foot." So when you're looking for a scale, that measurement will tell you the fraction of the real item's height as compared to the model. If you're looking at a 1/48 scale model, the real thing would be 48 times larger in each dimension. 28mm really doesn't tell you any of that.
To be fair, Wargames Factory has recently started producing miniatures that they are marking as 28mm as well as what their formal scale (1/56) is. However, most miniature manufacturers don't worry about that, and some of them will even be inconsistent in proportions between their own miniature lines (Compare Reaper's Dark Heaven line to their Warlord line sometime and you should see what I mean... Warlord figures tend to be a good 10-20% taller).
All blathering aside, the reason you're really reading this is not to get an idea of the business model or sculpting style of different companies. You want to know what you should be looking for on the shelf so that it will look good when you get it home.
The guest models in these shots are 1/48 humans that were included with some old Tamiya model kits in my collection. It's worth noting that the blue figure is supposed to be shorter than his compatriots, since he's the standard teen anime mecha pilot. You'll note that while the new figures are a little on the tall side, they're not unreasonable in context. That's because a convention of 28mm sculpting is to exaggerate some body features (like hips and facial features) in order for things to still look right at such a small scale. Because the width is similar, they look pretty good together.
Here, the guest models are 1/60 pilot models from old Bandai Gundam Mobile Suits. These models are downright tiny compared to the spokesmodels. Not only are they shorter, but they're also half as wide (if not thinner), which really demonstrates the scale difference between the figures.
The final guest models are 1/64 Farm Country figures from Ertl. There's really no way these figures could work, because they're just way too small. However, I thought it would be worth showing them, because 1/64 is the default scale for Matchbox and Hot Wheels cars. These figures will also make a comeback when I introduce some terrain pieces that were once highly sought after, and are now mostly garage sale fodder.
So there you have it... call it 1/55, but going a little bigger (to 1/50 or 1/48) should still look good for most items.
