Not sure what the mulch calculator was but if it is self explanatory than just take sqft of area divide it by 27 to turn into sq yards then multiply by depth. Ie: 2000 sq ft. 2000/27= 74. I want to mulch at 3 inch depth. 3/12 =.25 (percent of feet depth) take 74 x .25 = 18.5 yards of mulch.
If this isn't what is being talked about then disregard my comment.