Question
how do i measure the amount of top soil and organic matter to equal the depth of 4 to 6 inches on a 100 square foot area?

Answer
Spread your topsoil at a rate of 10-20 one-cubic-ft bags per 100 sq ft for a 1-2 in. depth -- or 40-80 one-cubic-ft bags for a 4-8 in depth.  Rototill or spade the topsoil thoroughly into the top 3-4 inches and you're in business.

Is that all?