Sentence Length Calculator

Average sentence length is one of the two inputs to almost every readability formula, alongside word complexity, and it is the one a writer can most easily control. General-audience web writing lands around 15 to 20 words per sentence; plain-language guidance for public information sits nearer 15; technical and academic writing routinely runs past 25. Comprehension does not fall off a cliff at any particular number, but it degrades steadily once sentences pass roughly 30 words, because readers have to hold more open clauses in mind before anything resolves.

The average alone hides the thing that matters most. A page averaging 18 words could be uniformly 18 — which reads as flat and mechanical — or could alternate between 8 and 30, which reads as varied and deliberate. Good prose has a wide distribution. What you are looking for is not a target average but outliers: the individual 45-word sentences that a reader has to restart. Those are usually two or three sentences that were never separated.

When a sentence is too long, the fix is rarely inserting a full stop at the midpoint. Long sentences are usually long because they contain multiple subordinate clauses stacked onto one subject, and splitting mechanically leaves a fragment. Find the second idea, give it its own subject and verb, and the sentence tends to divide naturally. Check the transition-word and paragraph-length tools alongside this one — uniformly long sentences and uniformly long paragraphs usually travel together.