As a rule of thumb, one should assume that a post A Round company will need to support a CEO, three VP's and 5 to 7 directors with incentive stock options from the stock option pool. And while circumstances vary widely to affect the proper amount of options to a position, the general consenus is the following for various positions:
CEO - Option Grant of 4 to 8%
VP's - Options of 2 to 3%
CFO - Options of 1to 3%
Directors - Options of 1/2% or less
All of which dictates a need for an option pool amount around 20% of the post A round share amount. Founder CEO's with shares or other particular facts may influence this and all generalizations are dangerous.
The right amount for any situation is and should be the focus of a fair amount of discussion.