Why Godzilla is so heavy?

Although some might try and chock it up as Toho not having a good grasp on measuring mass for their Kaiju, you have to remember that the larger an animal gets, the larger it becomes in overall mass exponentially, thus meaning it gets heavier overall as it keeps getting bigger and bigger. Factor in the fact that a Kaiju-sized creature is composed of denser and more heavy-set materials than an ordinary animal, and that further multiplies its mass to be proportionately larger than normal. The more realistic weights of the Kaiju in Pacific Rim, if you think about it, isn't as realistic for those sizes as some may believe.

Water Retension :P

Because he's Godzilla.

godzilla is ridiculously strong and dense, the density of his muscle and bone are the biggest contributers to his toughness, oh, and godzilla has been much heavier than that in some movies!

Because he's fat.

haha!

The opinion of THEGMAN123 is the true. The weights of TOHO, in relation with the sizes of they kaiju, are the most realistic of all. The weighs or Pacific Rim are exageratelly small, an animal of that height and weight "Slattern" will be like a huge bear (3 m tall) with the weight of a jaguar (120 kg)!!! It will break itself with a single strike of Godzilla's tail.

I blame Big Macs and soda. He is also know for long bouts of inactivity.

because he's huge

At a guess... I'd say that Snickers deal.

@Somthingreal

i think your spot on about the Pacific  Rim Kaiju. Also godzilla would have to be dense to support his weight.