With the decline of meta-tags, keyword density ranges have become very important. They’ve also become very controversial. Here’s the thing: you want a high enough keyword density—at least 7%--that your keywords rank highly in the bigger search engines, such as Google, Yahoo, DogPile, and HotBot.
But, as we discussed, you don’t want your keyword densities so high that they turn your content into over-hyped gobbledygook, nor do you want to raise a red flag when the spiders come crawling over your content. If your keyword density is 20% or more, the search engine will most likely red-flag you for “keyword stuffing” and penalize you by moving you down in the search results.
Thus, keyword density ranges are controversial. To make things worse, different search engines have different algorithms. One of them might thing an SEO keyword density of 18% is fine, another may not.
The only way a search engine can figure out just what your page is about is to search for the keywords you use. Those keywords don't necessarily have to be right there on the page—they can be in the title and in links that will lead to the page. Having said that, though, keywords that appear on your page are certainly the most common way that search engines use to decide what your page is all about. Keyword density refers to the ratio of keywords to the total number of words on the page.
Now I want you to look again at the paragraph above. There are 95 words total, and I used the word "keywords" exactly five times. The keyword ratio for the paragraph, then, is 5 divided by 95 times 100, or about 5.26%. Easy math, correct? You bet.
But how much does that stuff matter?
Well, it’s not a matter of life and death, but it’s pretty important. You see, when a search engine compares two pages to figure out which one ought to rank higher, keyword density will factor into it—usually pretty significantly. In fact, all other factors being equal (which is pretty much impossible, but let's pretend), the page with the higher keyword density will generally rank higher.
However, simple as Keyword Density is, it can also get really complex in a hurry. Do plurals or other stemmed variations of your keyword count as keywords? Should stop words, which are those common words you see all the time like "a" or "the," be ignored when calculating density?
Should you include off-page content, like meta tags and titles, in your calculations? What about keyword frequency or keyword proximity or keyword prominence? And like I’ve said before, bear in mind that if your keyword density gets too high, search engines just might realize it and penalize your page.
But now, hold on. Even though keyword densities are getting to be a complex science with lots of complicated algorithms, you can do it...
