How this calculator works
Firewood is sold by volume, not by weight, because the weight depends on how dry and how dense the wood is. The standard unit is the cord: a stack 8 feet long, 4 feet high and 4 feet deep, which is 128 cubic feet or about 3.62 cubic metres. The pieces in the stack are only as long as the logs were cut, so a stack that is one piece deep is a face cord, and its depth is simply the length of the pieces. Because split wood does not fill its stack completely, the solid wood inside a cord is usually only about two thirds to four fifths of the volume.
Formula
stacked volume = stack length x stack height x piece length. cords = stacked volume / 3.624556 m3. face cords = stacked volume / (8 ft x 4 ft x piece length in ft). solid wood volume = stacked volume x solid share. cost = cords x price per cord.
Worked example
A stack 2.4 m long and 1.2 m high, built from 40 cm pieces, has a volume of 2.4 x 1.2 x 0.4 = 1.152 m3. That is 1.152 / 3.624556 = 0.318 cords and about 0.968 face cords. At 70 percent solid content the solid wood is 0.806 m3, and at $400 a cord the stack is worth about $127.13.
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Frequently asked questions
How many face cords are in a cord?
It depends on the length of the pieces. A face cord of 16 inch wood is one third of a cord; with 12 inch pieces it is one quarter, and with 24 inch pieces it is one half. Divide the depth of the stack by 4 feet to see the fraction.
Is a cord the same everywhere?
The cord is 128 cubic feet across Canada and the United States. Some sellers advertise a "cord" that is smaller, so ask for the dimensions of the stack and measure it yourself if the price looks unusually low.
Why is only part of a cord solid wood?
Split pieces are irregular and leave gaps. The amount of solid wood ranges from about 60 percent for loosely thrown round wood to about 85 percent for well-stacked split wood. It affects how much heat the load actually contains.
Does seasoning change the volume?
Dry wood shrinks slightly, so a stacked cord of seasoned wood contains a little more wood per cubic metre than the same stack measured green. The difference is small compared with the gaps between pieces.