According to Alex Garcia, the producer for the film, Kong is going to be 100 feet tall.
And Legendary might have a problem on their hands because that means that Godzilla will be three and a half times taller than Kong (he's 350 feet tall in the 2014 film)... I guess Kong is going to have to climb the Empire State Building again just to stare back at Godzilla.
Funny thing, Shin Gojira has just been released in Japan and they had to make their Godzilla bigger than the Legendary Godzilla, by ten meters (Legendary's Godzilla was previously the largest Godzilla).
Basically this is happening:
So yeah.