A percentage of times a keyword used in a webpage compared to the total number of words on the page
you can use online sources and online calculation for result of keywords.
That is calculate with bounce rate or google analytical tool.
You can choose some tools for it.
How many time a keyword used in content it is based on that formulas.
KeywordDensity formula =(how many times you use perticular keyword/total words in the text)*100
Thanks guys for your replies
There is a formula of it you can check it out on google.
Nice thanks for giving such information.