Readability Score Checker
Score how hard your writing is to read with six standard readability formulas, and see which sentences are dragging the score down.
Every formula
Text statistics
Flesch and Flesch–Kincaid share two inputs and almost nothing else
Both read exactly two things — words per sentence and syllables per word. Divide each pair of coefficients and you get what the formula thinks an extra syllable per word is worth, measured in words per sentence:
| Formula | Coefficients | One extra syllable/word equals |
|---|---|---|
| Flesch ease | 1.015 · wps, 84.6 · spw | 83.3 words/sentence |
| Flesch–Kincaid | 0.39 · wps, 11.8 · spw | 30.3 words/sentence |
A factor of 2.75. Flesch thinks long words are nearly three times as damning as its own grade-level successor does. They are not two views of one measurement; they are two measurements that happen to share a surname.
And the five grades do not read the same text
| Formula | What it uses for "hard word" | Linear? |
|---|---|---|
| Flesch–Kincaid | syllables per word | yes |
| Gunning Fog | share of 3+ syllable words | yes |
| SMOG | 3+ syllable words per sentence | no |
| ARI | characters per word | yes |
| Coleman–Liau | characters per word | yes |
Three different ideas of what makes a word difficult — syllables, a count of long words, and plain character length — and exactly one formula that is not linear in its inputs. SMOG is the odd one out below, for that reason.
They agree on the order and disagree on the number
| Sample | FK | GUNNING | SMOG | ARI | CLI | Spread |
|---|---|---|---|---|---|---|
| plain | -2.6 | 1.3 | 3.1 | -5.7 | -7.5 | 10.6 |
| ordinary | 4.9 | 6.8 | 6.4 | 5.6 | 6.8 | 1.9 |
| technical | 31.6 | 36.3 | 26.0 | 34.7 | 38.1 | 12.1 |
| longSimple | 20.0 | 22.7 | 8.8 | 22.1 | 3.7 | 19.1 |
| shortHard | 40.6 | 36.8 | 12.5 | 36.6 | 44.9 | 32.4 |
On ordinary prose the five land 1.9 grades apart, which is fine. Push toward an extreme and they scatter: the shortHard sample pulls them 32.4 grades apart, because SMOG sees few words per sentence while Coleman–Liau sees very long ones.
Across 84 texts built with controlled sentence and word lengths, every pair of formulas correlates between 0.87 and 1.00 , with SMOG at the bottom of every low pair. As a way of asking "is this harder than that" they are nearly interchangeable. As a way of asking "what grade is this" they are not: the median gap between highest and lowest is 12.2 grades and the worst is 43.5.
So the averaged figure above is a reasonable summary in the middle of the range and a fiction at the edges. The spread is the honest statistic, and it is the one nobody prints.
One more thing about the ease score
Flesch ease is shown out of 100. The formula has no such bound. Of the samples above, 1 scores over 100 and 2 score below zero — the densest reaches -191 before the display clamps it. The clamp is right for a readout, but it is worth knowing it is a clamp: "0 out of 100" and "far below anything the scale was built for" are different findings, and the number cannot tell them apart. (The syllable counting underneath is its own can of worms, worked through on this site's syllable counter.)
How to use
- Paste at least a few paragraphs of text.
- Read the grade level and reading-ease scores.
- Look at the longest sentences flagged.
- Treat the scores as a prompt to reread, not a target to game.
Frequently asked questions
What do these formulas actually measure?
Sentence length and word length, essentially — nothing more. They count syllables per word and words per sentence, and combine them into a grade level. They do not measure clarity, logic, organisation or whether the writing makes sense, which is the single most important thing to understand about them.
What is a good score?
For general audiences, aim for a Flesch Reading Ease around 60 to 70, which corresponds to roughly an eighth to ninth grade level. Government and health guidance often targets sixth to eighth grade. Technical writing for specialists reasonably scores harder, and forcing it down would mean removing the terms that carry the meaning.
How is Flesch Reading Ease different from Flesch-Kincaid Grade Level?
They use the same inputs differently. Reading Ease gives a 0 to 100 score where higher is easier; Grade Level gives a US school grade. They rank texts almost identically, so reporting both adds confidence rather than information.
Can I cheat these scores?
Easily, which is why they should not be a target. Chopping every sentence in half and swapping long words for short ones improves the score immediately and can make writing worse — choppy, imprecise, and harder to follow. The score is a symptom to investigate, not a goal.
Why do the formulas disagree with each other?
Because they weigh their inputs differently and were calibrated on different material. Gunning Fog emphasises words of three or more syllables, SMOG was built for health materials, and Coleman-Liau counts characters rather than syllables. A spread of two grade levels between formulas on the same text is entirely normal.
Do they work on languages other than English?
Not without recalibration. Syllable counts and average word lengths differ by language, so an English formula applied to German or Spanish gives a meaningless number. Several languages have their own adapted formulas.
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