could somebody smarter than me figure out the following:

if i have X number of shares now and the stock gets diluted by a value of Y, i need to purchase Z amount of shares to retain my piece of the pie when i had X number of shares. this is for knowing how much % ownership they will have lost if they don't acquire more shares. this is probably an easy calculation but i don't really know the basics of this stuff. i'm asking this because i'm trying to decide when i'm going to add to my position. thanks!

chad