The only way a search engine can know what your page is about is to examine the keywords you use. Those keywords don't necessary have to be on the page (you can use keywords in the Title and in links coming to the page), but on-page keywords are certainly the most common way to determine what the page is about. Keyword density, in a nutshell, is the ratio of keywords to the total words on the page.

Look at the above paragraph again. There are 77 words total in the paragraph, and I used the word "keywords" exactly five times. The keyword ratio for the paragraph, then, is 5 divided by 77 times 100, or about 6.49 percent. Pretty simple stuff.

Is it important?

The best I can tell you for sure is that it's not unimportant. When a search engine compares two pages to determine which should rank higher, keyword density is going to play a role. Usually, a fairly big role. All other factors being equal (which is pretty much impossible, but let's pretend), the page with the higher keyword density will generally rank better.

As simple as Keyword Density is, unfortunately, it can also get really complicated really fast. Should plurals or other stemmed variations of your keyword be counted as keywords? Should stop words, those common words like "a" or "the," be ignored when calculating density. Should off-page content, like meta tags and titles, be included? What about keyword frequency or keyword proximity or keyword prominence? If your Keyword Density is too high, will the search engine penalize your page?

STOP!

This ain't rocket science, and it really doesn't need to be all that complicated. Go to Google and query for "keyword density" (no quotes, of course). The first three pages will give you a choice of about 20 or 25 different tools for calculating KWD. Pick one that feels comfortable to you and use it on your own optimized web page, noting the results. Now run a Google query on your keyword, and run the KWD analysis on the first ten sites, again noting the results. You now have a good idea how your page will compare with the ten top ranking pages in Google, at least in terms of keyword density.

If you were to do that with three or four of the KWD tools, you will almost certainly come up with different numbers, but the graph of those numbers will look amazingly similar. That's cool, because you don't really care about the numbers. You only care how they compare to each other.

Most of those questions that complicate keyword density don't matter as long as the answers to the questions remain the same. Each tool you use may answer those questions differently, but that will have minimal effect as long as you analyze all pertinent pages with the same tool and the same settings.

The possible complexities, in other words, are less important than being consistent.

One of the things you're going to discover is that keyword density is usually a poor indicator of rank. The top ranking page may have a much lower density than the page at number ten, for example. Again, that's because KWD is only one factor among many. It's important to a good ranking, but it's not enough for a good ranking. What you really want to know from your analysis is the range of density values that rank well. Chances are good that if your page is below that range, getting on page one will be tough, and if you're above that range, there is at least some danger of being penalized. Just remember, though, the numbers are guidelines you should know, not carved-in-stone rules that forever define your fate.

What about the oft heard advice that keyword density should always run between two and eight percent? Or whatever the numbers being quoted in forums across the Internet happen to be this week?

Those numbers are probably fairly accurate for most keywords. They are, after all, based on averages, and you won't go far wrong using an average range.

However ...

Did you know that the most often used letter in English text is the letter E? If you wrote a ten word sentence, it would be much easier to use the letter E five times in that sentence than it would be to use, say, the letter Q five times. The letters of the alphabet aren't necessarily distributed evenly, and golly gee, the same is true of keywords.

THE single most important thing about keyword density is that it read well and natural to a human being. It doesn't make sense, after all, to get a page one ranking if your content sucks. Like the letter E, some keywords are easy to use a lot while still sounding natural. Like the letter Q, some aren't. You can use an average range, which will work well most times, or you can analyze the top ten pages to find the best range for that particular keyword and be sure you're not trying to optimize for a Q.

Has anyone wondered why I asked you to do a search for tools instead of offering a list of links as I would usually do?

I think some people, perhaps even most people, like to know the rules. When they're driving down a country road, a posted speed limit can be quickly compared with their speedometer, and the sense of knowing they are close to that expected speed makes them feel comfortable. Similarly, knowing the range of keyword densities acceptable for a web page can go a long way towards establishing confidence.

Once you've driven the same road enough times, however, you probably don't look at your speedometer as often and you might not even notice those signs along the side of the road any more. Unlike the first few times you traveled this route, you've developed a feel for the road and know how long it should take to traverse.

I couldn't offer any advice on which KWD tools to use because I haven't used one in years, and I suspect you'll hear a lot of people in a lot of forums saying the same thing to you. At most, SEO veterans might look at a competitor's page in Google's cache (which highlights the keywords for you), or use similar features found in Firefox or the Google Toolbar, to get a good visual feel for density. Usually, though, I think most veterans rely a lot on reading all of our optimized content out loud a few times, always listening for that natural flow that will make the copy attractive to human visitors. If we can substitute a keyword for a pronoun without loosing that flow, we'll do it. If we put in a keyword and lose the flow, we take it out again. We've traveled the road often enough to know how it should feel.

When someone advises you to "just write naturally," it's certainly good advice, but it's not always really useful advice. It's a bit like telling someone to drive at a safe speed, which is also good advice.

Doesn't mean you can't look at the speed signs, though. :)

By Ron Carnell