If you repeat your keywords with every other word on every line, then your site will probably be rejected as an artificial site or spam site.

Keyword density is always expressed as a percentage of the total word content on a given web page.

Suppose you have 100 words on your webpage (not including HMTL code used for writing the web page), and you use a certain keyword for five times in the content. The keyword density on that page is got by simply dividing the total number of keywords, by the total number of words that appear on your web page. So here it is 5 divided by 100 = .05. Because keyword density is a percentage of the total word count on the page, multiply the above by 100, that is 0.05 x 100 = 5%

The accepted standard for a keyword density is between 3% and 5%, to get recognized by the search engines and you should never exceed it.

Remember, that this rule applies to every page on your site. It also applies to not just to one keyword but also a set of keywords that relates to a different product or service. The keyword density should always be between 3% and 5%.

Simple steps to check the density:
Copy and paste the content from an individual web page into a word-processing software program like Word or Word Perfect.
Go to the ?Edit? menu and click ?Select All?. Now go to the ?Tools? menu and select ?Word Count?. Write down the total number of words in the page.
Now select the ?Find? function on the ?Edit? menu. Go to the ?Replace? tab and type in the keyword you want to find. ?Replace? that word with the same word, so you don't change the text.
When you complete the replace function, the system will provide a count of the words you replaced. That gives the number of times you have used the keyword in that page.
Using the total word count for the page and the total number of keywords you can now calculate the keyword density.