A cord is the amount of wood that, when "racked and well stowed" (arranged so pieces are aligned, parallel, touching and compact), occupies a volume of 128 cubic feet (3.62 m3). This corresponds to a well-stacked woodpile 4 feet (122 cm) high, 8 feet (244 cm) wide, and 4 feet (122 cm) deep; or any other arrangement of linear measurements that yields the same volume.
In Canada, the cord is legally defined by Measurement Canada. The cord is one of three legal standards for the sale of firewood in Canada: stacked cubic metre, cubic foot, and cord. However the stacked cubic metre is now the preferred unit of measurement.
In the United States, the cord is defined by statute in most states. The U.S. National Institute of Standards and Technology Handbook 130, section 126.96.36.199, defines a cord and provides uniform regulations for the sale of fireplace and stove wood. In the metric system, wood is usually measured in steres and cubic metres: 1 stere = 1 m3 ? 0.276 cords.
Maine appears unique among U.S. states by also defining a "loose thrown cord" or pile of cut firewood: "A cord of 12 or 16 inches (30 or 41 cm) in length shall mean the amount of wood, bark and air contained in a space of 180 cubic feet (5.1 m3); and a cord of wood 24 inches (61 cm) in length shall mean the amount of wood, bark and air contained in a space of 195 cubic feet (5.5 m3). [1981, c. 219 (amd).]"
Other non-official terms for firewood volume include standing cord, kitchen cord, running cord, face cord, fencing cord, country cord, long cord, and rick, all subject to local variation. These are usually taken to mean a well-stacked pile of wood in which the logs are shorter or longer than in a legal cord, to accommodate various burners. For example, a face cord commonly consists of wood that is 16 inches (41 cm) long. The volume of a face cord therefore is typically 1/3 of the volume of a full cord even though it is 8 feet (244 cm) long and 4 feet (122 cm) high. A face cord is also called a rick in Midwestern United States.
The term is used in other English-speaking countries, such as New Zealand, but may not have a legal definition.
The corde was a unit of volume used before metrication in several French-speaking countries (France, Belgium and Luxembourg). Its value varied from 6 to 13.50 m depending on the region, corresponding approximately 2 to 5 steres. 
One seasoned (dry) cord of Northern red oak with a heating value of 22.1 million British thermal units per cord (6.4 GJ/m3) has the heating equivalent of 159 US gallons (132 imperial gallons; 602 litres) of fuel oil with a heating value of 138,700 British thermal units per US gallon (38.7 megajoules per litre).
A standard cord is a unit of measure of wood products 4 feet wide, 4 feet high and 8 feet long, or its equivalent, containing 128 cubic feet when the wood is ranked and well stowed. Any voids that will accommodate a stick, log or bolt of average dimensions to those in that pile shall be deducted from the measured volume.