Average sentence length, standard deviation, longest / shortest sentences, and a histogram of sentence lengths.
Built and maintained by Paul Clark, Redmoon Software
Use sentence-length analysis to spot monotonous rhythm — long passages of all-similar sentence lengths read as flat. Editors and writing coaches use it to push clients toward more varied syntax.
Sentence-length variety captures something Flesch and SMOG cannot: rhythm. Use it as a stylistic supplement to grade-level formulas.
This tool measures the mean and standard deviation of sentence length across your text.
A high standard deviation usually correlates with more engaging, varied prose — long sentences carry detail, short sentences punch.
Hemingway-style writing keeps average sentences around 12 words. Academic writing often runs 25+.
For most writing, 15–20 words per sentence reads well. Mix short and long for variety — high standard deviation usually correlates with engaging prose.
Strings of same-length sentences read as monotonous, while mixing short and long sentences creates rhythm and keeps readers engaged. A high standard deviation indicates good variety; a very low one suggests your prose may feel flat.
It measures how much your sentence lengths spread around the average. A larger value means you mix short and long sentences, while a value near zero means most sentences are nearly the same length.
Sentences are split on terminal punctuation such as periods, question marks, and exclamation points. Abbreviations, decimals, and ellipses can occasionally cause miscounts, so treat the totals as close estimates rather than exact figures.
Input
Short punch. Then a long, winding sentence that meanders through several thoughts and clauses before landing. Short again.
Output
Mean: 8.7 words, SD: 6.3 — High variety.
Three sentences of 2, 17, and 2 words. The high standard deviation is the signature of engaging, rhythm-aware prose.
An average sentence length of 18 words describes two completely different documents: one where nearly every sentence is 16 to 20 words, and one alternating 5-word sentences with 40-word ones. The first is monotonous. The second has rhythm. The average cannot tell them apart, which is why this tool shows the distribution rather than a single figure.
Variation is what makes prose readable at length. A short sentence after several long ones lands hard, and that effect is the main tool a writer has for emphasis. A document with low variance reads flat regardless of how good the average is.
The most actionable output is the list of longest sentences. Comprehension does not decline smoothly with length — it falls off a cliff somewhere past about 30 words, because that is where the reader runs out of working memory before the sentence resolves.
Long sentences are not automatically wrong. A 45-word sentence built from short parallel clauses is easy; a 25-word sentence with two nested subordinate clauses is not. Open the longest ones and check for nesting rather than trusting the count, and split the ones where the main verb arrives late.
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