cord of wood
A cord of wood is a pile of wood 4 feet by 4 feet by 8 feet neatly stacked as shown in the diagram. This gives a volume of 128 cubic feet, although there may be only 80 to 90 cubic feet of actual wood allowing for space between the stacked pieces. Bulk firewood is usually sold by the cord or fraction of a cord. A cord of wood, depending upon the type of wood and its dryness, generally weighs between 2 and 3 tons. As a rough guide, it will yield the heat equivalent of a ton of coal or 200 gallons of fuel oil. A typical full size pick-up, bed level, will hold about half a cord.
Be aware that in many states, a cord is the only legal unit that a seller can be held to if there's a problem. Sometimes wood is sold by the face cord, which is a stack measuring 4 feet high by 8 feet long. However, the depth can vary. If the pieces of wood are 4 feet in length, the face cord will be the same as a full cord, but if they're only half that length the face cord will be equivalent to a half-cord, and so on. Negotiate a price by the cord and you'll avoid confusion. Also be very cautious about buying wood on a weight basis because of uncertainty in the moisture content. Know whether the price is for green or air-dry wood.