You can calculate keyword density using the formula:
[Keyword/ Total Number of Words * 100%]
For example, the keyword density of the word “dogs” mentioned 5 times in 100 words of text is [5/100*100] = 5%.
Sometimes you have a long tail keyword phrase such as “adopt abandoned dogs” and it can be tricky knowing how to calculate the keyword density. The most popular method is to account for all three words in the string, so that “building dog houses” used 5 times in 100 words of text would be [5*3/100 *100%] = 15%.
Most industry guidelines will say that 3 to 5% is an appropriate keyword density per page.
However, we have found that keyword density is becoming less important as Search Engines have become more sophisticated. About 5 to 8 years ago content writing was very mathematical in that the right number of words had to be used throughout the text. As long as the target number was met the pages did well, regardless of the quality of the page content. A page written in this manner today would likely be read by Search Engines and marked as spam since the keywords are used not necessarily in context, but mainly for the sake of just being used.
Search Engines are much smarter today and are able to read and understand the context in which the keywords are being utilized. It is much more important to write content focused on a specific theme and remain relevant. Focus on the correct placement of keywords and how they are used in the text; never compromise clarity or a natural flow of speech for a precise keyword density.
Furthermore it is worth mentioning that some keywords may have a much higher density than others. For example, we recently optimized a website that sold golf packages. Obviously, the whole website was centered on golf and the words “golf”, “golfing”, “golf course” tend to have a much higher keyword density than just 3-5%. The Search Engines understand that this type of website is all about golf and do not penalize the higher than usual keyword density for the golf related words.