Method of Calculation: A Cord is defined as a tightly stacked pile of wood with the following dimensions: 4′ x 4′ x 8′. This volume (128 cubic feet) contains an average of 85 cubic feet of wood and 43 cubic feet of air. Each pound of wood contains 8660 BTU’s, but with well-seasoned firewood at 20% moisture, only 6200 BTU’s are available.
Example using Osage Orange: 57 lbs/cu.ft. x 85 (cu.ft./cord) = 4845 (lbs/cord) x 6200 (btu/lb) = 30 (mbtu/cord)