Cord of Wood Converter

A cord is a volume of stacked, not solid, wood: 128 cubic feet, the space filled by a rank 4 feet high, 8 feet long and 4 feet deep. Because round split pieces cannot pack perfectly, only about 80 to 90 cubic feet of that is actual wood fiber, the rest being air, so two identically legal cords can differ by roughly ten percent in fuel content depending on stacking and split uniformity. Any stack converts by multiplying its three dimensions in feet and dividing by 128. A face cord or rick is 4 feet high by 8 feet long but only as deep as the pieces are long, so a 16-inch face cord is one third of a full cord. Heat content scales with dry mass rather than volume, which is why species matters. Air-dried at about 20 percent moisture, hickory yields roughly 26 to 28 million Btu per cord, red oak and sugar maple around 24 million, ash and cherry near 20 million, and yellow pine about 17 million. For comparison, one million Btu is about 7.2 gallons of heating oil at 138,500 Btu per gallon, or 10 therms of natural gas. Two caveats dominate: green wood at 50 percent moisture wastes a large share of its energy boiling off water, and appliance efficiency ranges from perhaps 30 percent in an open fireplace to 70 percent or more in a certified stove, so delivered heat is far below the raw cord figures.

The word cord refers to the line once used to measure a stacked rank of fuel wood, and the unit long predates industrial fuel markets. The four foot by four foot by eight foot rank was established English practice before it was carried to the American colonies, and its dimensions were practical rather than arbitrary: four feet was a comfortable stacking height, and four foot cut lengths could be handled by one worker and split down later for the hearth. As firewood moved from farm use to a commodity hauled into towns, the cord became the basis for delivery contracts, tolls and taxes. Legal enforcement came with weights and measures regulation. In the United States firewood is a regulated commodity, and the model rules published in NIST Handbook 130 and adopted by most states require that it be advertised and sold by the cord or a decimal fraction of a cord, with terms such as rick, face cord, truckload or pile prohibited as the sole basis of sale precisely because they carry no fixed volume. Btu-per-cord tables, the other half of any firewood comparison, came later and largely from forest products laboratories and university extension services, which measured oven-dry density by species and converted it to heat content at a standard moisture level. That is why extension tables from different states agree closely on rankings even where their absolute numbers differ.