That might sound vaguely impressive until you convert that to more standard units- three foot six inches, or just over one meter.
As Sam Vimes learns in Guards! Guards!, Gayheart Talonthrust was considered a bit of a freak, as most male swamp dragons (cobbs) don't get bigger than 8 thumbs, or 2 feet. Female swamp dragons (hens) are a bit smaller. This proves beyond doubt that the giant Noble dragon attacking the city is definitely not a swamp dragon.