Keyword density is the share of a text occupied by a target keyword, expressed as a percentage. The formula is:
keyword density = (keyword occurrences / total words) × 100%
Worked example: an 800-word article that uses the phrase "running shoes" 8 times has a keyword density of 8 / 800 × 100% = 1%. For multi-word phrases, tools usually count phrase occurrences against total words, though some count against total phrases of the same length; the exact denominator is a convention that varies, so compare tools consistently.
The concept comes from SEO. In the early days of search, cramming a keyword onto a page could lift rankings, so writers pushed density high. Modern search engines have long since moved to semantic and intent-based ranking, so there is no magic number and no target to optimise toward. A loose, healthy range for a primary keyword is often cited as 0.5%–1.5%, but this is a symptom of natural writing, not a lever to pull. The real risk is the other direction: density above roughly 3% reads as keyword stuffing, looks spammy to readers, and can get a page deprioritised. A common misconception is that hitting a specific density improves rankings — it does not; writing naturally for the reader and covering related terms and phrases matters far more. Keyword density analysis usually ignores stop words so that "the" and "of" do not dominate the results. Measure density and spot over-used terms across your draft with our word frequency counter.