how much do an impression?
The average earnings across the whole of the Google Publisher Network is often said to be $1 per 1,000 ad impressions. Only Google really know how accurate that figure is, but if it were correct and your site performed to that average then you would receive $100 for your 100,000 ad impressions. That average isn't a very good indicator though. In practice performance varies hugely from one site to the next.