if the web site is 100 Page impressions per day No ad Clicks How much we will earn? With out click ads how much Page impressions We need?
Googles blog is a good place to start for your answers, try this one for starters: http://adsense.blogspot.com/2006/02/ecpm-what-exactly-is-that.html
CPM = cost per M (M = 1000 in roman) impressions eCPM = effective cost per thousand impressions = (earning/impressions) x 1000. It is also the effective earning per M impressions
It's impossible to say how much you can earn based on the impressions and clicks, because the $$ varies depends on keywords, visitor location,etc.