The 3 numbers do relate to size across motor to motor, a 250 is 250mm from motor to motor, a 330 is 330mm and so on, if you are after a try before you spend out good money they syma is ok but the jjrc h8c is very good, I got one for Christmas and it's awesome for the money and has built in camera for video or stills, probably get about 15 mins flight out of a battery as well which isn't bad. It performs flips and rolls really easy too, think these are