keyword efficiency index
Also called: kei, keyword effectiveness index
Keyword Efficiency Index (KEI) is a legacy SEO metric that scores a keyword's opportunity by dividing its search volume (squared) by the number of competing pages. A higher KEI flags keywords with strong demand and light competition, so it works as a fast way to shortlist targets.
SEO practitioner Sumantra Roy coined KEI in the late 1990s to shortlist keywords for the search engines of that era. The core idea: reward demand, penalize saturation.
The formula
The original score is KEI = (P² / C) × 1000, where P is keyword popularity (search count) and C is the number of competing pages. Squaring popularity is deliberate. When two keywords share the same volume-to-competition ratio, the one with more searches gets the higher score, so KEI leans toward bigger traffic. Roy built it on three axioms: KEI rises as popularity rises, falls as competition rises, and rises when both grow in the same proportion.
A common reading of the output treats scores under 10 as weak, above 10 as workable, and above 100 as strong. A term with 1,200 monthly searches and 45,000 competing pages scores roughly 32 on the unscaled volume² / competition form.
Treat the number as a first-pass filter, not a verdict. KEI counts competing pages but says nothing about how strong those competitors are, whether the searcher wants to buy, or whether a SERP feature eats the clicks. Different tools plug in different competition inputs (total results, allintitle, or a difficulty score), so two KEI figures for the same keyword rarely match. A high KEI alone does not earn a ranking, since Google weighs hundreds of signals the formula never touches.
How it affects your traffic
KEI can rank a keyword list in seconds, but it scores a page that converts and one that never will exactly alike as long as the arithmetic looks good. It ignores search intent, competitor authority, SERP features, and whether the traffic buys anything, so leaning on it alone pushes effort toward cheap, empty terms. Used as a rough shortlist it saves time; used as the decision it wastes it. This is where SEO consulting earns its keep, layering intent, real difficulty, and revenue potential on top of the raw ratio so the keywords you chase actually feed pipeline instead of vanity traffic.
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