How tall is a 125cc dirt bike?

it depends. there are many sizes and difrent kinds of 125's. Every single bike is diffrent. look at the suzuki RM125 which is about 37.4 inches in seat height. then look at another brand of 125, like the Yamaha ttr125 is only 30.5 inches. if it is a pit bike, it might only be about 20 inches. depending on the bike