The scale of a figure is meant to be a measure of an average human male in that particular miniature line. So if a manufacturer lists it's figures as 25 millimeters, a standard 6' tall male would be represented as a 25mm figure. Females of course will be slightly smaller and taller figures will be larger. Hypothetically that is...
The average historical male stands 5'4". Modern heights in the USA are 5'9" for males and 5'4" for females. That is not something that anyone takes into account though.
Games Workshop provides many convenient examples of scale problems. Their lines are listed as 28mm. The average sized human figures in its Warhammer 40,000 range are the same size as the space marine models, which are supposed to be eight feet tall. Assuming that their "average size" figures really were 28mm, a space marine would be 37mm tall by comparison. GW most likely doesn't want to redo the Space Marine line because it would render nearly two decade's worth of models obsolete and alienate many long time gamers. And GW would never do that.
Miniatures are sometimes measured using the Barrett Scale. The Barrett Scale takes into account the height of the figure from the soles of the feet up to eye level. It is also supposed to include a letter indicating whether the figure is (S)light, (M)edium, or (H)eavy. So a figure listed as 26H would be 26mm tall at eye level and thick. This letter is often omitted though.
Other manufacturers simply use the total height of the figure, from the bottoms of the feet to the top of the head. Since most companies do not list the type of measurement they use, consumers are left to fend for themselves. Two different 28mm figures from two different companies may not be the same height, and may look rather odd next to each other on the table-top, even though they are supposedly the same scale. Even figures from the same company can look out of place next to each other due to sculptors'style differences. Take a look at these two figures from Reaper's Dark Heaven line, sculpted by Sandra Garrity and Werner Klocke(respectively). Although they are about the same height, the head and hands of the figure on the right are about 50% larger than those of the figure on the left. Figures with exaggerated don't always fit well with more realistic figures.
The size of a figure's head in relation to it's total height is known as "head ratio." Obviously there are differences in real people, but an average person is roughly seven and a half heads tall. Miniatures are quite different. What is accepted as normal are figures who are about 5 heads tall. The smaller the head ratio, the more stocky and cartoony the appearance of a figure. The most poignant examples are Rackham's dwarves, who come in at 1.5-2 heads tall. Some Fenryll figures are as much as 9 heads tall. Generally speaking a larger head ratio will result in a more slender, elegant looking figure. This is one of the reasons that Rackham looks so different when compared with other major manufacturers.
The height of the base can also add to the disparity in appearance between two figures. Figures that come attached to their bases generally have a base thickness of 1.5-3mm while Games Workshop-style slotted bases are generally about 4mm in height. So a true 28mm figure on a 2mm base will have a total height of 30mm while a Barrett Scale 28mm figure on a slotted base will be closer to 34-35mm in total height. The good news for collectors is that this can be used to your advantage as shorter figures can be given larger bases to ease some of the disparity that may exist.
Traditional miniature scales have been 15mm and 25mm for many years. While most historical miniatures still use these two scales, fantasy and science fiction genres are a bit more varied. And some companies use more obscure 5mm, 6mm, 10mm, or 20mm. Back in the late eighties and early nineties, companies like Games Workshop, Ral Partha, and Grenadier produced 25mm figures. By the mid-nineties, Games Workshop's figures were 28mm and the many in the fantasy industry followed suit. The figures that GW has released over the last couple of years are still called "Heroic 28mm," but are 28mm in name only. Many are 29-30mm Barrett Scale even though the figures generally are slightly crouched with their feet spread wide apart. If the figures could be stood upright, that would add another 2mm or so in height. And again many companies have followed suit. Rackham has popularized the 35mm scale in the last few years. The human figures in it's Confrontation line are supposed to measure 35mm from head to toe, and many of the Confrontation figures are much larger than human. To be fair though, they do not claim to be 25mm. Again many companies have followed suit and now even 40mm figures are on the horizon. 40mm is closer to 54mm than it is to 25mm! The reason for the increased scale is simply that companies continually try to outdo each other with larger, more detailed, more impressive looking figures. Bob the Barbarian King may be a great looking 28, but loses some of his luster if he's placed next to 35mm tall Trooper Joe from another company. And of course it's much easier to sculpt a 35-40mm figure than it is to sculpt a 25mm figure.
Why do many companies still claim that their figures are "Heroic 25mm" or "Heroic 28mm" when they regularly produce figures that are 30-32mm Barrett Scale? The main reason is marketing. 28mm doesn't sound too bad compared with 25mm, the longtime industry standard. But 25mm and 30mm? That sounds like a much bigger difference. And 25mm and 35mm? That's a 40% difference. So in order to avoid scaring off us skittish consumers, who generally like our figures to be somewhat compatible, the 25mm and 28mm titles remain.
Shown below are miniatures from various manufacturers. Included with the figures are the listed scale (LS), Barrett Scale height (BS), actual height (AH), and total height including the figure's provided base (TH). All measurements are listed in millimeters. Height for figures does not include hats, top knots, etc. As you can see, the worst offender is actually Reaper Miniatures. They list their Dark heaven and Warlord lines as "Heroic 25mm," but many of their figures are 30-31mm at eye level. Their Warlord figures are all around 35mm tall. Maybe everything really is bigger in Texas...
Manufacturer Figure LS BS AH TH
1. Rackham Keltois Warrior 35 34 37 41
2. Games Workshop Space Marine 28 28 31 36
3. Reaper Lindir 25 30 33 36
4. Games Workshop Gandalf (LOTR) 25 27 29 33
5. Old Glory German Barbarian 25 26 30 31
6. Hobby Products Empire Hero 15 16 17.5 20
7. Rackham Paladin 35 33 36 40
8. Games Workshop Catachan 28 29 31 35
9. Games Workshop Scout (early 90's) 25 25 27 30
10. Reaper Boris the Black 25 30 33 36
11. Foundry German Barbarian 25 29 31 32