The guy that played Conan in the recent remake was about seven foot tall, and 320 pounds. Do you think that a seven foot space marine, even with denser muscle mass, is going to double that (320kg is about 600 lbs.)? Maybe, maybe, I mean, SCIENCE - These guys spit acid. But to QUADRUPLE that and weigh 1200 pounds? I don't frikkin' think so. A 1200 pound, 7, 8, or even NINE foot tall guy would NOT be fit by any sense of the term. I seriously doubt he could even support himself, increased bone density or no. You'd have to step way out of the established height of a Space Marine to make a 1200 pound guy that makes any sense.

But see, I have a great explanation for how these numbers work. They don't, and should be ignored, or you should stick to the lower end of the scale.

This is not a religious text. It's a table 'o' Fluff in an RPG rule book. Growing marines would be a very significant detail, and would not have been completely left out of ALL other materials just to be mildly hinted at in an optional table in the Character Creation chapter.

I read somewhere that these guys have ceramite in their diet to reinforce their bone structure, they have 2 hearts, 3 lungs, 2 stomachs, 2 times more muscles than a normal human... So who knows if it's possible or not. Anyway that's my explanation of the rules and nothing says it's not so. I didn't make it to convince people, I made it for my own game and shared it here so that people take in it what they want. I respect everyone's view on this matter but, even if Orks grow it doesn't mean Marines should not, even if you say it's not possible I still can't think of any other explanation...

As Space Marines are often seen same size on pictures, the movie "Ultramarine" and so on... The only other option I see is decreting that all are 2, 20 meters naked (if 2, 30 meters with Mk VII armour could be seen as "a bit more than 2, 10 meters") and weighting all 320 kg without armour, because then they would still weight "between 500 kg and 1000 kg" (500 with Mk VII armour and 720 with Terminator)... I don't like it much but it's an option. Because if what they say in the rulebook about size is wrong then, what is not you know...

Whilst the link to the article about Astartes growing over time has some merit, i think it is vastly exaggerated. Your average battle brother spends a lot of his 'down-time' undergoing further hypno-doctrination, training and a chemical therapy to maintain his various implants and organs and keep him in top shape. If the Imperium has the technology to hyper-accelerate bone, muscle and tissue growth in a 15 year old teen to turn him into a 7 foot tall super soldier, then i think it's perfectly acceptable that they'd standardize height so that power armour didn't need adjusting every few years or so.

Yes, Terminators may be a bit bigger and bulkier, but i think that is more indicative of the sorts of battle brothers that end up earning a place in their chapter's first company - they are big and strong by even Astartes standard, and have weathered a thousand battlefields, testing their mettle and their steel against untold powerful foes of the Imperium.

So yeah, i don't think it's reasonable to say that a marine grows an entire foot over time without regulation, and if there were regulation there would be something printed in fiction SOMEWHERE to support the idea that marines grow bigger in order to use Terminator armour.