British Thermal Unit ratings are units of measure used to determine the heat of combustion of firewood. These numbers are a rough comparison of different types of firewood and depend on the species of tree, its burn and the season.
The combustion of firewood is measured in millions of BTUs per cord, where each cord is a stack of firewood 8 feet long, 4 feet wide and 4 feet high. Apart from the type of wood, its moisture content determines its heating capabilities. BTU charts provide a comparison of different types of firewood to aid in making the right choice.