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Flesch reading ease calculator

The formula worked through step by step, with your own numbers in it

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The calculation

206.835 − 1.015 × (words / sentences) − 84.6 × (syllables / words)

Paste text to see every term of the formula calculated against it.

Where the numbers come from

Rudolf Flesch published this in 1948, and the three constants - 206.835, 1.015 and 84.6 - were fitted against reading-comprehension test results rather than derived from anything. That is why they look so oddly precise. They are a curve fit, not a theory.

What the formula assumes is simple and mostly true: longer sentences are harder to follow, and longer words are harder to read. What it cannot see is everything else - whether the sentences are in a sensible order, whether the words are the right ones, whether the argument holds together at all.

Two ways to move the score

  • Split sentences. The sentence term is weighted 1.015 per word of average length, so cutting your average from 25 words to 18 adds about 7 points.
  • Shorter words. The syllable term is weighted 84.6, which makes it the more powerful lever by far - dropping average syllables per word from 1.7 to 1.5 adds about 17 points.

That weighting is why swapping "utilise" for "use" moves the number more than you would expect, and why technical writing scores low no matter how short the sentences get: the vocabulary is the constraint.

Score, or fix?

This page shows the arithmetic. If you want to know which specific sentences are dragging the score down, the readability checker lists them.

Common questions

What is the Flesch Reading Ease formula?
206.835 minus 1.015 times the average words per sentence, minus 84.6 times the average syllables per word. Rudolf Flesch published it in 1948. The three constants were fitted to reading-comprehension test data, which is why they look arbitrary - they are empirical, not derived.
Why can the raw score go above 100 or below 0?
Because the formula is unbounded. "Go. Run." scores above 100; a single long polysyllabic word scores well below zero. The 0 to 100 range is a convention describing where ordinary English prose lands, not a limit the arithmetic enforces. We show the raw result and the clamped one separately.
How is Flesch-Kincaid Grade Level different?
Same two inputs, different constants, and the scale is inverted. Reading Ease goes up as text gets easier; Grade Level goes up as it gets harder, and is expressed as a US school year. Grade Level is 0.39 times words per sentence, plus 11.8 times syllables per word, minus 15.59.
How are syllables counted?
By vowel-group counting with corrections for silent trailing e and for the -ed inflection, which only adds a syllable after t or d - "parted" is two, "raced" is one. It is a heuristic, wrong on roughly one word in twenty, mostly compounds and Latin borrowings. That is fine for a banded verdict and would not be fine for a precision instrument.
Can I use this on languages other than English?
No. The constants were fitted to English, and the syllable heuristic is English orthography. Other languages have their own adaptations - Fernandez-Huerta for Spanish, Amstad for German, Kandel-Moles for French - with different constants entirely.