The cord is the typical measurement for firewood. It is a stack of firewood measuring four feet by four feet by eight feet. The standard cord is usually not used as four foot pieces don't fit in stoves. You will usually be sold a face cord (4'X16"X8').
It is hard to know what you pay for in firewood unless you measure the purchase. It should be stacked for a full cord or a half cord. A full cord will be a stack 4' x 4' x 8'. It should be stacked for an accurate measurement with the volume at 128 cubic feet.
It measures 4 feet high by 4 feet wide by eight feet long (4' x 4' x 8') and has a volume of 128 cubic feet.
A cord of wood is 4x8 feet long and is wide as individual firewood pieces. A common fraction of cord has pieces averaging 16" and is equal to 1/3 of a full cord.