Google Adsense allows a maximum of three standard ad units, two Adsense for Search boxes, three Adsense link units and three Adsense referral units to be placed on any web page.
The program policy says:
Related: Adsense Tips for Improving Revenue
The program policy says:
Currently, AdSense publishers may place up to three AdSense for content units on one web page. you may also place a maximum of three link units and two search boxes on each web page.The Adsense Bible also says - "No Google ad may be placed on pages published specifically for the purpose of showing ads, whether or not the page content is relevant."
You may place up to three link units on a page, in addition to the three standard ad units and two search boxes that.
If you place more than one ad unit on a page, our system will display unique ads to each ad unit. Because the system automatically displays an optimal number of highly targeted Google ads on each page, in some cases, the maximum number of ads may not always appear. In this case, the ad unit will be displayed as a transparent box or will contain any alternative ad or colour specified in the ad code.
Related: Adsense Tips for Improving Revenue