Flesch Reading Ease
A readability index that maps a text to a 0–100 ease scale using two surface predictors: average sentence length and average syllables per word. Higher scores mean easier text. Published by Rudolph Flesch in 1948 in the Journal of Applied Psychology paper A New Readability Yardstick, and the parent of the more familiar Flesch-Kincaid Grade Level (Kincaid et al. 1975), which kept Flesch's two predictors and re-expressed them on a US-grade scale.
The formula
Flesch derived the coefficients by regressing the two predictors against the McCall-Crabbs Standard Test Lessons in Reading, the standard 1925 corpus of grade-calibrated reading passages. The constant 206.835 is the regression intercept; the negative coefficients ensure that longer sentences and longer words push the score down.
The interpretive bands
Flesch published a verbal description of each 10-point band, and these bands have stuck despite decades of revision attempts:
- 90–100: very easy (5th grade)
- 80–90: easy (6th grade)
- 70–80: fairly easy (7th grade)
- 60–70: standard / plain English (8th–9th grade)
- 50–60: fairly difficult (10th–12th grade)
- 30–50: difficult (college)
- 0–30: very difficult (college graduate)
Scores can fall below 0 or rise above 100 in extreme cases. Reader's Digest sits around 65, the Harvard Law Review around 30, the King James Bible around 85.
Strengths and limits
The strength is communicative directness. A 0–100 ease score is intuitive in a way that a grade-level number never quite is, and Flesch's verbal bands give writers a target without requiring familiarity with US grade conventions. This is why FRE is the readability number embedded in Microsoft Word's spell-check pane and in most consumer writing tools.
The limits are the same as every surface-feature formula. FRE has no sensitivity to vocabulary frequency, anaphoric distance, topical demand, or rhetorical structure. A text with short sentences and short syllables can score 70 and still be hard for an L2 reader who lacks the schema the writer assumed; a long-sentence narrative can score 50 and remain accessible. For ELT use FRE is a coarse first filter, useful in combination with discourse-level measures and human CEFR judgement, never as a sole arbiter.
Why FRE and FKGL give different verdicts on the same text
The two indices share the same predictors and the same regression base, so their rankings of texts are nearly identical. They disagree only in scaling: FRE is a continuous 0–100 ease scale, FKGL is a US-grade scale, and a text that is "easy" by Flesch's bands corresponds to a grade level by Kincaid's recalibration. Citing both on the same text is largely redundant. They drift apart most visibly on extreme texts: very long sentences with very short words, or the reverse.
Inter-tool variance on FRE typically runs 1–5 points across implementations on identical text — almost entirely from differences in syllable estimation. See Text Metric Implementation Variance for the mechanisms.
Key References
- Flesch, R. (1948). A new readability yardstick. Journal of Applied Psychology, 32(3), 221–233.
- Kincaid, J. P., Fishburne, R. P., Rogers, R. L. & Chissom, B. S. (1975). Derivation of new readability formulas (Automated Readability Index, Fog Count, and Flesch Reading Ease Formula) for Navy enlisted personnel. Naval Technical Training Command Research Branch Report 8-75.
- DuBay, W. H. (2004). The Principles of Readability. Impact Information.
See Also
- Flesch-Kincaid Grade Level: the grade-mapped sibling of FRE
- Readability: the broader construct and what surface formulas miss
- Gunning Fog Index / SMOG / Dale-Chall Readability Formula: the other three formulas FRE is most often reported alongside
- Text Metric Implementation Variance: why FRE scores drift 1–5 points between tools on identical text