Rob, its as Fred says. My units are 28mm figures sized/based for a 15cm grid. You can have bigger units in a smaller figure scale or a smaller grid. I looked at 6, 10 and 15mm before a mate convinced me to go 28mm as he already had some. In hindsight I should probably have gone 15mm as 28mm pikemen are a pain! I've attached a photo of two of my units.