In the late 1990s, the early days of search engines, keyword density was an important factor in page ranking.
The formula to calculate your keyword density on a web page for SEO purposes is
, where Nkr is how many times you repeated a specific keyword, and Tkn the total words in the analyzed text.
A "keyword" consisting of multiple terms, e.g. "blue suede shoes," is an entity in itself.
The purest mathematical representation should adjust the total word count (Tkn) lower by removing the excess key(phrase) word counts from the total: Density = ( Nkr / ( Tkn -( Nkr * ( Nwp-1 ) ) ) ) * 100. where Nwp = the number of terms in the keyphrase.