Keyword density is the proportion of words on a page that are a particular keyword or phrase, normally expressed as a percentage. If “boiler repair” appears six times in an 800-word page, a simple calculation puts its density at 0.75%.
How keyword density works
The basic sum is the number of times the phrase appears, divided by the total word count, multiplied by 100. In practice every tool counts slightly differently. Some treat a two-word phrase as one occurrence, others count both words. Some strip out common words such as “the” and “and”. Some include the menu, footer and cookie banner in the total, others only the main copy. The same page can therefore show 1.2% in one checker and nearly 3% in another, and neither figure is wrong.
In the early days of search, engines leaned heavily on how often a word appeared, which is why density became an obsession. Modern search systems read language far more like a person does. They recognise plurals, synonyms, related phrases and the topic of the page as a whole, so repeating an exact phrase adds little once the page clearly says what it is about. Google has said for years that it has no ideal percentage, and nothing in its documentation suggests one.
Why it matters
Density is still worth a glance because it catches two opposite problems. The first is a page that never actually names what it offers. I often see service pages from UK firms written in soft brand language, such as “we help you make sense of your numbers”, that never once says “accountant” or “Self Assessment tax return”. A reader skimming the page, and a search engine matching it to queries, both have less to go on.
The second problem is the reverse: a phrase repeated so often that the copy reads badly. At that point the issue becomes keyword stuffing, which Google treats as spam, and which puts off the people you want to convert. A British spelling point applies here too: checkers count “optimisation” and “optimization” as different words, so a page written in British English may look as though it under-uses a term that a US-based tool expects in American spelling.
Common mistakes
- Writing to a percentage. Rules of thumb such as “aim for 2%” date from an older era of search and turn sentences into word puzzles.
- Forcing the exact phrase. Lines like “best plumber London cheap” are written for a counter, not a customer. Natural variants do the same job.
- Counting the body and ignoring placement. Where the term appears matters more than how often. The title tag, the H1 and the opening paragraph carry far more weight than a fifth mention halfway down.
- Repeating it everywhere else. The same phrase in every image’s alt text, every subheading and the footer adds clutter without adding meaning.
- Treating the checker as a quality score. A page can have a textbook density and still fail to answer the question the searcher brought.
How to act on it
Write the page for the reader first, then check three things. Does the main term appear in the title, the H1 and the first paragraph, in words a customer would use? Does the copy use the natural variations and related vocabulary that anyone explaining the subject would use, which is what semantic search rewards? And does any single phrase stand out when you read the page aloud?
The readability and keyword density checker lists the most frequent words and phrases on a page, which makes outliers easy to spot. If one phrase sits far above everything else in that list, reread those sentences and vary them. If the main term barely appears, the page probably needs to be clearer about what it offers. Balancing this across titles, headings and copy is part of the routine work in on-page SEO.