I currently have 1 google ad on each page of my websites, but I was wondering if I was to put 3 adverts on each page (The limit google adsence allows), for each user to go onto the page, would I get 3 page impresstions, or 1?
It still counts as 1 page impression. Through Advanced Reports you can "Show data by" ad unit, or even individual ad.
if you have all the ads as same, then it would be one impression. if you have multiple ad block with seperate channels, then each channel will have its own impression