Board Thread:Warhammer 40k General Discussion/@comment-86.10.75.96-20160401182432/@comment-92.238.70.22-20170312011203

The weight of power armour is stated directly in Codex: Angels of Death to be over 250 lbs, so going on ~115 kg by metric reckoning. To my knowledge, this is the only official statement on the matter. It noted in the same passage that the earliest marks were heavier as they lacked efficiency improvements and more advanced materials that became available during the crusade. The fact that this would limit a space marine in their armour plus equipment to be somewhere under the mass of three typical adults (so, in the range of 250 kg) would also justify them not routinely having problems with falling through any floor that isn't specially reinforced.

The plates of ceramite forming the bulk are also stated to be "up to an inch thick", and have a honeycomb structure to localise any damage to a few cells - something in line with modern Chobham ceramic composite armour off things like the Challenger and Abrams tanks, and indicated in the magnification bubble on the old RT-era illustration you can see in the main article.

Interestingly, as well as the fibre-motivated bundles negating the suit mass, Codex: Angels of Death states that most suits incorporate a "gravitic energy damper" that reduces the effective weight and inertia of a suited marine to "that of a normal human being", which would make them unbelievably fast and agile given the strength of a marine is way beyond a normal human, as well as being extremely useful if they needed to fight over, say, an icefield without disappearing into the first thinly covered fissure.