How big is a life-size dragon?

1.How long is an adult dragon?

The little cute ones can be as small as 2 feet long

usually 30 feet although the famous ones are bigger (Imagine St George slaying one with a sward)

A respectable dragon should be at least 300 feet long, about a city block.

I would expect something several blocks long.

Probably half a mile although hard to tell because it's usually wrapped around mountains and such.