As far as I know the standard keyword density is 3%. In that case, if you write an 1000 word article, you can use your keyword phrase 30 times. If your density is 2% you can use it 20 times.

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There are two main ways to calculate keyword phrase density.

A=Total occurrences of the keyword phrase in the article
B=Total number of words in the article
C=Number of words in the keyword phrase

Keyword density calculation 1 uses:
(A / B) * 100

Keyword density calculation 2, uses:
(A * C / B) * 100

Let’s have a look at an example and the difference in the keyword density score those two formulas can make.

Let’s say we have a article with 1000 words and using keyword phrase of “search engine results page” (4 words) where there are 10 occurrences of that phrase.

So using the first formula, that gives us:

(10 / 1000) * 100 = 1% keyword density

and using the second formula, gives us:

(10 * 4 / 1000) * 100 = 4% keyword density

This is one of those times where you are going to have to sacrifice keyword density.

A 1,000 word article with a 4-word keyword showing up 30 times? That will not read well...

Optimizing shorter articles is MUCH easier than longer ones. By the time you get to 1,000 words, you just aren't going to have a high density unless your keyword is 1-2 words long or it gets completely over-used.

You should really be writing for both the search engines AND people. Make sure your keyword is in the title, and more importantly the anchor text. After this, just try to fit it in as much as you can without it being repetitive.

I think 3% to 4% is the best keyword density level....