Why is the "cord" the standard unit for firewood?

Cord is to firewood as barrel is to oil. An old form of measurement that has stuck.

"Cord of wood" dates back hundreds of years. You can search the origin of the term. It's odd and doesn't make a bunch of sense today. Today by weight would be accurate and ideal. Knowing what wood it is and it's weight you could caculate things like btu. But how much would it cost to convert to that system of measure? Hauling the scale to the delivery site would be a nightmare. Dry times would have to be in a controlled environment. The cost of a cord would probably double.

Wood pellets stack well and sold by weight. They are the "future" in firewood sort of speak. Not that firewood is going anywhere.

Using the word as a unit of measurement, “cord” is traced back to the 1610s when wood was sold in bundles tied with a, you guessed it, cord. Today, it is well recognized that a cord of firewood must take up 128 cubic feet, traditionally in a stack 8′ x 4′ x 4′.

If you go by weight it is problematic because the moisture content of the wood changes (you want to pay for the wood not the water). So that's why they use a volume measurement instead. 4x4x8 is perhaps arbitrary but it's just a convenient way to measure it and it stuck.

it has to do with being a redneck mostly ... thats about the size a pickup holds ..