📖 Readability Score Checker

A readability checker scoring Flesch Reading Ease, Flesch–Kincaid, Gunning Fog and Coleman–Liau — and listing the sentences that produced the score.

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What Readability Score Checker Does

Readability formulas all work the same way: they count sentence length and word difficulty, and combine the two into a number. Flesch Reading Ease runs 0 to 100 with higher meaning easier; Flesch–Kincaid converts the same inputs into a US school grade; Gunning Fog estimates the years of education a reader needs. None of them read your text — they count it.

That is worth understanding because it tells you what moves a score. Both Flesch measures are driven by average sentence length and average syllables per word, and nothing else. Gunning Fog swaps syllable average for the proportion of words with three or more syllables. Sentence length is the term all three share, which is why splitting long sentences changes a score far more than swapping vocabulary.

So the useful output is not the number, it is which sentences produced it. This lists your longest ones, because a text scoring badly usually has a handful of sprawling sentences rather than uniformly hard prose, and fixing three of them can move every score at once.

One honest caveat about all of it: these formulas measure how demanding prose is to decode, not whether it is any good, accurate or worth reading. A text can score beautifully and say nothing at all.

How to Use Readability Score Checker

Paste or type your text
View readability scores in real-time
Check the grade level and difficulty assessment
Adjust your text for your target audience

Formula Used by Readability Score Checker

The three formulas

Ease = 206.835 − 1.015·ASL − 84.6·ASW Grade = 0.39·ASL + 11.8·ASW − 15.59 Fog = 0.4·(ASL + 100·(complex ÷ words))

ASL: average sentence length — words divided by sentences
ASW: average syllables per word
complex: words of three or more syllables — Gunning’s own definition, and syllables rather than letters

Worked example

A 200-word passage in 10 sentences, 320 syllables, 24 words of three or more syllables.

ASL = 200 ÷ 10 = 20; ASW = 320 ÷ 200 = 1.6
Ease = 206.835 − 1.015×20 − 84.6×1.6 = 206.835 − 20.3 − 135.36
Grade = 0.39×20 + 11.8×1.6 − 15.59 = 7.8 + 18.88 − 15.59
Fog = 0.4 × (20 + 100 × 24÷200) = 0.4 × (20 + 12)

Result: Ease 51.2 (fairly difficult), grade 11.1, Fog 12.8 — all three saying roughly "late secondary school".

Flesch Reading Ease, interpreted

Score	Level	Typical of
90–100	Very easy	Writing for young children
80–89	Easy	Conversational English
70–79	Fairly easy	Popular fiction
60–69	Plain English	Where most general-audience writing aims
50–59	Fairly difficult	Quality journalism, trade press
30–49	Difficult	Academic and professional writing
Below 30	Very difficult	Legal and technical documents

What actually changes a score

All three formulas share average sentence length, which is why it dominates.

Change	Effect
Splitting a 40-word sentence into two	Large — it moves the term every formula shares
Cutting one long sentence entirely	Large
Replacing "utilize" with "use"	Small, unless done throughout
Removing a subordinate clause	Moderate — shortens the sentence and often drops long words
Adding headings and paragraph breaks	None to these scores, though it genuinely helps readers

How to Read Your Result

Aim for a range, not a number

General audiences are usually well served somewhere in the 60s on Reading Ease, which is around a 9th-grade level. Technical documentation for specialists can sit lower without being a problem. Writing to hit an exact score produces stilted prose, which is the one thing that reliably makes text harder to read.

Short samples give unstable numbers

These are averages, so a handful of sentences can swing wildly — a single long one moves everything. Below about five sentences the figure is arithmetic rather than information, and the tool says so rather than presenting it as a finding.

Syllable counting is an estimate

Without a pronunciation dictionary, syllables are approximated by counting vowel groups with corrections for silent endings. It is what these formulas assume and it is not exact — "business" counts as three here and is two in speech. Small differences between readability tools almost always come from this.

Limitations & Accuracy Notes

English only. The coefficients were derived for English and produce meaningless numbers for other languages.
Syllables are estimated rather than looked up, so counts differ slightly between tools.
The formulas measure decoding difficulty, not clarity, accuracy, structure or value.
They ignore everything that genuinely helps a reader: headings, lists, paragraph length, and whether the sentences are in a sensible order.
Lists, code blocks and tables are treated as prose, which distorts the sentence average.
Proper nouns and familiar jargon are counted as complex words, which Gunning’s original definition excludes — no automated tool can reliably tell which is which.

Frequently Asked Questions

What is a Flesch-Kincaid score?

The Flesch-Kincaid readability test estimates the U.S. school grade level needed to understand a text. A score of 8.0 means an 8th-grader can understand it. Lower scores = easier to read.

What readability score is ideal for web content?

For general web audiences, targeting a 7th to 8th grade reading level (Flesch-Kincaid score around 60–70) ensures maximum clarity and user engagement.

Which score should I pay attention to?

Flesch Reading Ease is the most widely recognized and the easiest to explain to someone else. Gunning Fog maps roughly onto years of education. They usually agree on direction, so the informative signal is whether an edit moved the score, not its absolute value.

What score should I aim for?

It depends entirely on the audience. General web writing often targets a reading ease around 60 to 70; technical documentation for specialists will score much lower and should. Writing toward a number rather than toward your reader produces worse text.

Why does my technical writing score badly?

Because these formulas count syllables and sentence length, and accurate technical vocabulary is polysyllabic. "Authentication" is four syllables whether or not it is the correct word. A low score on specialist writing often means it is precise, not that it is bad.

Can a readability score be gamed?

Trivially — chopping every sentence in two and swapping long words for short ones improves the score without improving anything else. That is the clearest evidence these are surface measures, useful as a prompt to reread rather than as a target.

Do these formulas measure comprehension?

No. They measure two proxies for difficulty and are blind to organization, coherence, accuracy, and whether the argument makes sense. A passage of fluent nonsense in short sentences scores well.

Is my text sent anywhere?

No. All analysis runs in your browser.

References & Further Reading

plainlanguage.gov — Federal Plain Language Guidelines — What actually makes government and professional writing readable, most of which no formula measures
Readable — the Gunning Fog Index — States the formula and the three-or-more-syllables definition of a complex word

By OnlineToolHubs Team • September 2026