Sentence Counter
Sentence-boundary detection that handles abbreviations, decimals, and ellipses correctly.
Counting sentences sounds trivial — just count the periods, right? — but real writing is full of periods that don't end a sentence: "Dr. Smith arrived at 3:30 p.m." has three periods and one sentence. This tool applies a set of rules to tell genuine sentence-ending punctuation apart from decimal points, abbreviations, and initials, so the count reflects actual sentences rather than raw period tally.
It matters for anyone checking prose rhythm: an essay made of consistently long sentences reads very differently from one with short, punchy ones, and average sentence length is also the backbone of most readability formulas (see /blog/readability-scores-explained/ on the blog).
Sentence count appears here as you type.
0
Sentences
0
Words
0
Avg. words/sentence
Why sentence counting is genuinely harder than it looks
The counter treats a period, question mark, or exclamation point as a sentence boundary only when it's followed by whitespace and a capital letter (or the end of the text) — and it maintains a short list of common abbreviations (Mr., Mrs., Dr., Jr., Sr., St., vs., etc., e.g., i.e., and a few others) that it does not treat as sentence-enders even though they end in a period.
Decimal numbers like "3.14" or "$19.99" are recognized because the period sits between two digits with no space — that pattern is excluded from sentence-boundary detection entirely, regardless of what follows.
Ellipses ("...") are treated as a single boundary marker rather than three separate ones, and are only counted as ending a sentence if followed by a capital letter or paragraph break — mid-sentence trailing-off ellipses ("and then... nothing happened") are correctly left uncounted as sentence boundaries.
No heuristic is perfect: unusual formatting, quoted dialogue with punctuation inside quotation marks, or abbreviations not on the built-in list can occasionally throw the count off by one or two sentences on a long document. Treat the number as a very close estimate rather than a hand-count guarantee.
Who uses this
- Checking average sentence length against a target for accessible or plain-language writing (shorter average sentence length is one input to most readability scores).
- Spotting a section of a draft that's become one long run-on by comparing sentence count against word count.
- Academic or technical writing checks where a style guide caps sentence length or count per paragraph.
Edge cases to know about
- Dialogue with punctuation inside quotation marks ("Stop!" she said.) is generally handled correctly, but heavily stylized or unconventional punctuation (like text written entirely in lowercase with no terminal punctuation) will undercount, since there's no boundary marker to detect at all.
- Bullet-point lists without terminal punctuation on each line are not reliably counted as separate sentences — pair this tool with the /line-counter/ or /paragraph-counter/ if your text is list-formatted rather than prose.
- Abbreviations not on the built-in exception list (foreign-language honorifics, uncommon technical abbreviations) may be miscounted as sentence boundaries; if you notice the count is consistently high on a specific document, check for one of these.
Related tools
FAQ
- Does it count a sentence fragment ending in an exclamation point?
- Yes — question marks and exclamation points are treated as sentence-enders the same way periods are, since grammatically they close a sentence whether or not it's a complete independent clause.
- What counts as one sentence in a list of bullet points?
- If each bullet ends with terminal punctuation and starts with a capital letter, each is generally counted as its own sentence. Bullets without terminal punctuation may not be detected as separate sentences at all — the /line-counter/ tool is a better fit for counting list items specifically.
- Why did my count go up by exactly one after I added a title?
- A title without terminal punctuation is usually not counted as a sentence at all (correctly), but if you added terminal punctuation to it, it will now be counted as a very short sentence, which can also shift your average-sentence-length figure noticeably on short documents.
- Why is average sentence length shown alongside the count?
- Average sentence length (total words divided by sentence count) is one of the core inputs most readability formulas use, alongside average syllables per word — a document made of consistently long sentences scores as harder to read than one with the same word count broken into shorter sentences, even if the vocabulary is identical. See /blog/readability-scores-explained/ for how that figure feeds into a full readability grade.