In case you didn't get that the first time around, how about a visual?
This picture is the woodpile at the Husker Barn here on Arington Tree Farm. The red diagram shows the dimensions of a full cord of wood, or 128 cubic feet (click the photo to enlarge it). Let's do some math!
A cord is four feet high, and four feet deep and eight feet wide. 4'x4'x8'=128 cubic feet of wood. A half cord is still four feet high and four feet deep, just half the width. 4'x4'x4'=64 cubic feet of wood. The dimensions of a face cord is four feet high and eight feet wide, but only the depth of sixteen inches. 4'x8'x16"=42.6 cubic feet. Firewood is commonly cut to sixteen inch lengths. The full cord is three rows deep while the face cord is only one row deep.
Here on the farm, we cut firewood to eighteen inch lengths, because we have a large wood boiler that can handle that size. If you do the division, you will quickly realize eighteen inches doesn't evenly go into four feet. So if we wanted to calculate the size of our woodpile we would have to do it by volume. The woodpile is an average of four feet high, twenty-five feet deep and thirty-five wide. 4'x25'x35'=3500 cubic feet. 3500 cubic feet woodpile/128 cubic feet per cord= 27.3 cord woodpile.
That's a lot of math for a Friday morning!