Can I use same Google adsense code on multiple sites?

Question

or do I need to generate separate ad for each site?

Answer 1

You dont have to generate separate ad code for each site, code once generated will work on all sites and click are counted by Google.

but with this you will not be able to trace which site is performing good. better create a channels and use ad code.

Answer 2

If you use the same code on multiple sites, you can use Google Analytics to show stats for different sites.

But you don't even have to do that now, because the new version of AdSense reporting gives you analysis by sites on the advanced reports. You don't have to setup custom channels or do anything else. Just click the beta test link in the top right of the AdSense admin area.