Firewood Cord & Rick Calculator
Enter your wood pile dimensions to get the exact cord equivalent, face cord count, cubic metres, and BTU heat content. Annual heating estimate included. Nothing uploaded.
Wood Pile Dimensions
Annual heating estimate
Results
Full cord = 4ft × 4ft × 8ft (128 cubic feet stacked). Face cord = one-third of a full cord (4ft × 8ft × 16in logs). Always buy by full cord equivalents, not by truck-load descriptions.
Learn more: cord, face cord and BTU math
What a cord is
A full cord is 4 feet by 4 feet by 8 feet, or 128 cubic feet (3.62 cubic meters) of stacked wood. Utah State University Extension defines it as an evenly stacked pile containing 128 cubic feet of wood and air space, so the figure includes the gaps between logs.
The calculator treats a face cord as one third of a cord: the same 4 by 8 foot face, stacked about 16 inches deep. That is 42.7 cubic feet. A 4 by 4 by 8 foot stack is therefore 1 cord and 3 face cords, while an 8 by 4 foot face stacked 16 inches deep is 1 face cord, or 0.33 cord.
Heat content by species
The calculator uses approximate air-dried heat content per cord, for example 28 million BTU for oak, 25 for maple, 24 for ash, 22 for birch and 17 for pine. USU Extension's wood heating table lists dry-weight values in the same range, such as 29.1 for white oak, 24.2 for white ash, 20.8 for birch and 15.9 for white pine.
The same page notes that green firewood may contain 50% or more water by weight and gives less heat, because heat is spent boiling the water off. The figures above assume seasoned wood.
Estimating a winter's wood
The annual estimate multiplies floor area by 10 BTU per square foot per degree-day and by your climate's degree-days. It then divides by a stove efficiency of 65% and by 23 million BTU, the figure for mixed hardwood.
A 1,500 square foot home in a cold climate (6,000 degree-days) needs 1,500 x 10 x 6,000 / 0.65 = 138 million BTU, which is about 6 cords. The 10 BTU figure and the 65% efficiency are rough assumptions, and an older or draughty house can need more.
FAQ
How many BTUs are in a cord of firewood?
It depends on the species. The calculator uses about 28 million BTU for a cord of oak and 17 million for pine, so the same heat takes about two thirds more pine by volume than oak.
Why does stove efficiency matter?
Not all the heat in the wood warms the room. At 65% efficiency, the rest goes up the flue, so the annual estimate divides the home's heat demand by that figure instead of using the wood's raw BTU content.
Is a face cord always a third of a cord?
Only when the logs are about 16 inches long, which is what the calculator assumes. A face cord with longer logs holds more wood, so check the log length and the stack dimensions when you compare quantities.