What the Sentence Length Analyzer does
This analyser counts the words in every sentence of your text and draws them as a rhythm chart, so you can see at a glance where the long sentences are, whether the lengths vary enough to hold attention, and how the average compares with the target you set. Long sentences are listed longest first, and one click selects each one in your text so you can split it.
An average alone hides the problem. A letter can average 20 words a sentence - a common plain-English target - and still contain two 60-word sentences nobody will follow. The chart, median and long-sentence list show what the average does not. Everything updates as you type and stays in your browser.
How to use it
- Paste your text or load an example. Results appear straight away and update as you edit.
- Set your target average and the thresholds for long and very long sentences. The defaults - a 20-word target, 25 words as long and 35 as very long - follow common plain-language advice; GOV.UK, for example, advises 25 words or fewer.
- Read the rhythm chart from left to right: each bar is one sentence, in order. Orange bars are long, red bars very long, and the dashed line is your target.
- Work down the "Sentences to split first" table. Select in text puts the cursor on that sentence in the box, ready to edit.
- Check the variety notes: a run of sentences that are all nearly the same length is flagged even when none of them is long.
Reading the results
The median is the middle sentence length. When it is far below the average, a few very long sentences are pulling the average up - fix those first.
Spread (SD) is the standard deviation of sentence lengths, and the variety note divides it by the average. Very low variety reads as monotonous; very high variety usually means a handful of sprawling sentences among short ones. The bands used are A2Z rules of thumb, not a published standard.
Sentences of three words or fewer are shown as fragments in the CSV. Fragments are fine in moderation - "We are sorry." is a complete, useful sentence - but a page of them feels abrupt.
Worked example: a council letter about missed bin collections
Load the council letter. It has 8 sentences and 165 words, so the average is 20.6 words - almost exactly on a 20-word target. On the average alone the letter looks fine.
The sentence lengths in order are 8, 5, 58, 3, 7, 7, 72 and 5. The median is 7 words, and two sentences - 58 and 72 words - carry more than three-quarters of the text. They explain why collections were missed and what happens at Easter, which are exactly the parts readers most need to understand.
The chart shows two red spikes among short bars, the variety note flags a very uneven text, and the table lists the 72-word sentence first. Splitting each spike into three or four sentences leaves the average similar but makes the letter far easier to follow.
Formulas and scoring rules
- Average sentence length
mean = total words / sentences- Median
middle value of the sorted lengths; the mean of the two middle values when the count is even- Spread
SD = sqrt( sum((length - mean)^2) / sentences )Population standard deviation - the whole text, not a sample.- Variety
CV = SD / meanA2Z bands: below 0.25 low variety, 0.25-0.6 healthy, above 0.6 very uneven.
How sentences and words are counted
A sentence ends at a full stop, question mark or exclamation mark followed by a space and a capital letter, digit or quotation mark. Common abbreviations such as Dr., Mr., e.g. and i.e. and initials such as J. K. do not end a sentence, and neither does the point in a decimal. A line break before a capital letter also starts a new sentence, so headings and list items are counted on their own.
Words are runs of letters and digits, with apostrophes and hyphens kept inside a word, so "don't" and "well-known" count once. Figures with a decimal point count as two tokens. Different tools make different choices here, so expect small differences from a word processor's count.
Limitations: what the result does not prove
- Length is not the same as difficulty. A 30-word sentence built as a clear list can be easier than a 15-word sentence full of jargon; use the Plain Language Analyzer for word choice.
- Sentence detection is rule-based. Unusual punctuation, missing spaces after full stops or text pasted from PDFs with broken lines can merge or split sentences.
- The thresholds are conventions, not rules. Legal, academic and technical writing often runs longer; set the targets to suit your audience.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- Inside GOV.UK - Sentence length: why 25 words is our limit
- US federal plain language guidelines - write short sentences
Frequently asked questions
What is a good average sentence length?
For general readers, 15-20 words is a widely used target, and plain-language guides advise keeping most sentences under about 25 words. The right figure depends on the audience: technical specialists tolerate longer sentences, while web and mobile readers skim and prefer shorter ones.
Why does my text feel choppy even though sentences are short?
Because variety matters as much as length. A run of sentences that are all four or five words long sounds abrupt. The analyser flags runs of three or more sentences within two words of each other so you can merge a pair or add a longer one.
How long is too long for one sentence?
There is no hard limit, but past about 25 words readers start to lose track of the subject, and past 35 most people need to re-read. Those are this page's default thresholds, and you can change them to suit legal, academic or children's writing.
How do I shorten a long sentence?
Look for joints: "and", "which", "because", "although" or a semicolon usually mark where one idea ends and another begins. Split there, make each part a full sentence, and move any list of conditions into bullet points.
Does it count headings and bullet points as sentences?
A line break followed by a capital letter starts a new sentence, so headings and bullet items are counted separately rather than being glued onto the next paragraph. If you want to analyse body text only, paste it without the headings.
Is the text I check for sentence length stored anywhere?
No. The analysis runs in your browser as you type, and nothing is sent to a server or stored. You can check this in your browser's network panel: the page makes no request when you edit the text.
Last reviewed by the A2Z.Tools team against the sources listed above.
