The average human skull is about 9 inches tall. When you put the two models together, you can see a pretty decent lack of size difference. So lets take a comparative look at marines and Imperial Guardsmen from the tabletop. For example, looking at the first picture, we can see that a marine should stand almost 2 feet taller than that of an average human. We all know the scale of the tabletop miniatures is a little off. There is a really interesting thought that popped up in my head though. I thought they gave a decent look at the scale of a Space Marine pretty decently. I found these when digging around on the interwebz.