The folks over at Fuel Interactive have released a somewhat practical PPC ROI calculator.

The utility's target user base:
Publishers who have yet to begin their PPC campaigns and just want to dabble in ROI forecasts, as well as those seeking to optimize existing campaigns.

Information you'll need to populate and run the calculator:
  • Monthly Ad Spend
  • Conversion Rate
  • Cost Per Click
  • Average Sale

For additional information on this utility, how to populate it, and how to interpret the metrics, checkout the Search Engine Journal article on the topic:

The PPC ROI Calculator: How To Forecast And Optimize Your PPC ROI