Jon Peltier's article on bubble chart bubble sizes may help you:

http://peltiertech.com/Excel/Charts/...bbleSizes.html

Juan wrote:
I am trying to map the position of plants using X and Y coordinates and the
area cover by each plant using the diameter in a bubble chart of Excel, but
the graphs look unrealistic. I would like to know what is the equation Excel
uses to calculate the size (area) of each point in the bubble charts so that
I can adjust my size parameter.
Thank you so much,
Juan


--
Debra Dalgleish
Excel FAQ, Tips & Book List
http://www.contextures.com/tiptech.html