That’s a slightly controversial topic among AT players.
People started calling it “8mm” after a GW employee said that a Space Marine would be 8mm tall during a presentation. Using the old “Xmm” scale convention, that would be a little bigger than 6mm, but certainly less than 8mm. And indeed, the Adeptus Titanicus titans scale out to imprecise numbers between 1:230 and 1:280. It’s that broad a range because we have canonical heights for them in meters, but the models are too posable for an easily standardized measurement and they aren’t consistent with each other. The Warhounds are on the larger end - they’re overscaled compared to the Reaver and Warlord. That’s probably why they don’t work well with Battletech minis.
To continue the AT scale discussion… it’s common to refer to Z-scale as 1:220 and as 7mm. I don’t think the math quite works out - if 6mm is 1:285, then 7mm should be 1:244; there’s some rounding going on. Either way, it puts the game in the 6-7mm range. I just think of it as 6+ mm.
