How big are 0 gauge trains?

HUUUUUUGE and tiny like an ant

Actually the track is 1.25 inches wide. It is about half the size of the first train models called "Standard Gauge" and was developed to accommodate model toy trains in the smaller homes that were being built after the turn of the century. The engines and cars are about an inch and a half wide and up to 15 inches long depending on the original being modeled.