Here's one.... Multiply H'xW'xL', then divide by 128 to give you a cord amount or fraction of a cord. Why can't you? http://www.maine.gov/ag/firewood.html
Basic math: one standard cord measure is 4'x4'x8' = 128 cu. ft. But they can be any dimension. As Papa says, divide your 3 dimensional stack measured in feet by 128 to get the number of true cords. Example: I have a face cord 4' high by 8' long by 16 inches wide. 16 in. = 1.33', so 4' x 8' x 1.33' = 42.66 cu ft. 42.66/128 = .33 or 1/3 of a cord.
Does anyone actually use the cord calculators? It would take longer to look one up then to do the math.
I forgot to mention it, but the resource has been made and it links to the Maine calculator mentioned in this thread.