Count sentences and analyze average sentence length instantly. Free online sentence counter with readability insights. Free, private, in-browser.
A sentence counter analyzes text to count the number of sentences and provide statistics about sentence length. It helps writers, editors, and students understand the structure and readability of their text at the sentence level.
Sentence length directly impacts readability. Research shows that average sentence lengths above 25 words make text harder to follow, while very short sentences (under 10 words) can feel choppy. The sweet spot for most content is 15-20 words per sentence, with variation for rhythm.
Academic writing typically averages 20-25 words per sentence. Journalism aims for 15-18 words. Marketing copy often uses 10-15 words for punch. Legal writing can exceed 30+ words but is widely criticized for poor readability.
Vary your sentence length. A mix of short and long sentences creates rhythm and keeps readers engaged. After a long, complex sentence, follow with a short one. It works. Use this tool to identify if your text lacks variety — if all sentences are within 2-3 words of the average, consider varying them.
The tool splits your text at periods, question marks, and exclamation marks, then measures the words between those boundaries. That rule matches ordinary prose closely, but it has known edge cases worth understanding so you can read the numbers correctly. Abbreviations such as "Dr.", "Ph.D.", "e.g." and "U.S." each end in a period, so a paragraph packed with them reports more sentences than a human would count. Decimal numbers like 3.5 behave the same way. Ellipses are treated as one boundary rather than three. Text with no terminal punctuation at all — a heading, a bullet fragment, a pasted list — is treated as a single sentence.
Because of this, sentence statistics are most reliable on continuous prose: essays, articles, reports, and chapters. If you paste a table of contents or a reference list, expect the average length to look artificially short. Strip those sections out before measuring and the figures become genuinely useful.
The average alone can hide a problem. A document averaging 18 words per sentence sounds healthy, but if the longest sentence is 61 words and the shortest is 3, the reader is being thrown between extremes. Compare the three figures: when the longest sentence is more than roughly double the average, at least one sentence is doing too much work and should be split at its first conjunction.
The opposite pattern matters too. If the longest, shortest, and average sentences sit within two or three words of each other, the prose has no rhythm. Readers experience that as monotony even when every individual sentence is correct. Deliberately shortening one sentence in every five restores the cadence without changing your argument.
Readability research consistently links sentence length to comprehension because working memory has to hold each clause until the sentence resolves. Around 14 to 18 words, most readers follow a sentence on the first pass. At 25 to 30 words, comprehension drops noticeably for a general audience. Past 40 words, readers routinely reverse and re-read, which is the point at which a reader on a phone tends to abandon the page.
Sentence length is also a direct input to the formulas that grade text. Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog, and SMOG all combine average sentence length with a measure of word complexity. That means shortening sentences improves every one of those scores at once, and it is usually the fastest available fix — far quicker than replacing technical vocabulary that your audience may legitimately need.
Find the first "and", "but", "which", "because", or semicolon after the twentieth word and end the sentence there. Most over-long sentences are two complete thoughts joined out of habit, and splitting them costs nothing. Next, look for nested clauses set off by commas: if removing a clause leaves a grammatical sentence, that clause can usually become its own sentence or move to the end.
Turn buried verbs back into verbs. "The implementation of the policy resulted in a reduction of costs" carries three abstract nouns and runs to eleven words; "the policy cut costs" says the same thing in four. Converting passive constructions to active voice removes the "by" phrase and its supporting words. Finally, cut the throat-clearing openers — "It should be noted that", "In terms of", "The fact that" — which add length before the sentence has said anything.
Sentence statistics tell you where structure is failing; a readability score tells you how the whole document rates. The efficient workflow is to measure sentences first, split anything far above your target, then run a readability check to see the effect. Because sentence length feeds directly into those formulas, the improvement is usually visible immediately, and you avoid rewriting vocabulary that was never the problem.
Your text is analyzed entirely in your browser. Nothing is uploaded or stored, which makes the tool safe for unpublished manuscripts, client reports, and confidential drafts. You can verify this by opening your browser's network panel while typing — no request is made.
Want a full word count? Try our Word Counter. Check overall readability with the Readability Score Checker, examine characters with the Letter Counter, or review keyword balance using the Keyword Density Checker.
Sentences are split by periods, exclamation marks, and question marks. Abbreviations like 'Dr.' or 'U.S.' may cause slight miscounts.
Text without sentence-ending punctuation is treated as a single sentence.
Average sentence length affects readability. Most style guides recommend 15-20 words per sentence for general audiences.
Yes, as long as the language uses periods, exclamation marks, or question marks for sentence endings.
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