Usually the fire rings at campgrounds are small to LIMIT the size of the fire.  They don't want you to have a huge fire. 

Now as a Boy Scout we would just put rocks in a circle and put the fire in the middle.  We could make the fire ring however big we wanted.  Like TMMMull said you need fuel and oxygen.  For a ceremonial fire we made a fire that was about 10 feet in diamater and about 5 feet tall.  A few guys worked all day Saturday building the fire for Saturday night.  The interior of the fire was a log cabin style that allowed a big air pocket in the center and then a teepee style on the outside.  They wrapped a tow chain around the top to keep individual logs from falling over as it burnt.  That fire went up quickly, burned hot, bright, and fast.  The flames were pretty tall as well.  If you try to do that in a State Park you will be seeing a Park Ranger real fast  :ranger: