KEI is a term used often in SEO. It stands for Keyword Effectiveness Index or Keyword Efficiency Index. If you do SEO at all, you’ve probably ran across this term.

KEI is a formula that compares the search volume, and competition of a keyword to create a number that is an indication of the keyword’s effectiveness.

KEI helps you identify keywords that are going to be the most effective in generating traffic. A keyword with a high KEI will assist you in pinpointing your real competitors. The ideal keyword will have high demand and low competition – so the higher the KEI, the better chance you have to get the keyword to rank on SERP.

The most popular way to calculate KEI is:
# of searches per month ^ 2/#of search results for the keyword query