Chapin, Kaiser, and Godschalk (Urban land use planning, 1995) address how to do this on p. 329. Basically, the short cut way is to get total employment data by category, and divide the number of employees by acres of land use in that employment category to get a rate of employees per acre. This source also notes that years ago the gross employment density in Charlotte ranged from 8.9 employees per acre in the outer, newer employment centers to 51 in the central business district.
I'm not sure I can fully justify it, but office workers use about 200 or 300 square feet of space per employee, and if you had gross square footage data you could use that. Retail would be higher, but I don't know exactly how much. See also the discussion about industrial employment densities in Urban Land Use Planning, p. 330. 8 per acre is a reasonable suburban ballpark figure and the range has been shown to be from as low in Phoenex to as high as 24 per acre for industrial employment. Since employment density will vary from place to place it is best to do a local study.
Jerry Weitz