You can find free online tools and more professional paid utilities that can do a keyword density analysis.

http://www.searchenginepromotionhelp.com...

Google doesn't publish any guidelines for optimal keyword usage, the advise comes from SEO people making an educated guess from their experience as to what percentage of the content may be a single keyword. the ultimate value of pushing the limits of keyword use may no longer be worth it, in the new world of the Penguin filter Google recently introduced to expressly identify search optimization tricks, it ma prove that simply writing quality content for your users has the greatest value.

Here are some insightful articles on this new filter:

http://www.seomoz.org/ugc/5-penguinfrien...

http://www.seomoz.org/blog/penguins-pand...

Keyword density doesn't matter. Just make sure your keyword is listed on your page twice. I never worry about it and rank first for a number of phrases.

Hi Install search Status to your browser and check every thing included keyword density..

Firefox browser plus the free seo quake plugin, and then click on the info, and it will give lots of information.