Measuring readability: what the Flesch score and the Vienna formula show
Readability formulas estimate how hard a text is from two things: how long the sentences are and how long the words are. The German Flesch formula by Amstad gives 0 to 100 (higher is easier, 60 to 70 is “standard”); the Vienna formula gives roughly a school grade from 4 to 15. They do not judge content, structure or tone.
The formulas at a glance
Flesch (German, Amstad 1978)
180 − ASL − 58.5 × ASW
ASL = words per sentence, ASW = syllables per word. 0–100, higher is easier.
Flesch (English, 1948)
206.835 − 1.015 × ASL − 84.6 × ASW
Same inputs, weighted for English. Used here for English texts.
1st Vienna formula (1984)
0.1935 MS + 0.1672 SL + 0.1297 IW − 0.0327 ES − 0.875
MS = % words with 3+ syllables, SL = words per sentence, IW = % words over 6 letters, ES = % one-syllable words.
Making a web text easier to read
- 1.Split long sentences: one statement per sentence. The check shows the longest ones.
- 2.Replace long nouns with verbs: “to apply” instead of “the submission of an application”.
- 3.Say who does what: active instead of passive where the actor matters.
- 4.Cut filler words that add nothing to the statement.
- 5.Put the answer first, then the details: on screen many people read only the start of a paragraph.
What the check cannot do
Syllables are counted with a rule of thumb: vowel groups, the diphthongs ei, ie, au, eu and äu as one syllable, plus some exceptions such as -lie (Familie) or loanwords like Website. Words such as Museum or Ideen can be off by one. Sentences end at full stops, question and exclamation marks and line breaks; common abbreviations like z. B. are recognised. Passive voice is detected with a word-list heuristic and can be wrong, e.g. with future tense. A good score does not make a text good: content, structure and tone matter more.
Readability check: frequently asked questions
What is the Flesch Reading Ease?
A score from 0 to 100 calculated from the average sentence length and the average number of syllables per word. Higher means easier. Rudolf Flesch published the formula in 1948 for English; Toni Amstad adapted it to German in 1978 because German words have more syllables on average.
Which formula does the check use?
For German texts the Amstad formula 180 − ASL − 58.5 × ASW and the first Vienna formula (Wiener Sachtextformel). For English texts the original Flesch formula 206.835 − 1.015 × ASL − 84.6 × ASW. ASL is words per sentence, ASW syllables per word. The language is detected roughly from common words; you can set it by hand.
What does the Vienna formula tell me?
It was developed by Richard Bamberger and Erich Vanecek for German non-fiction. It combines the share of words with three or more syllables, the sentence length, the share of words longer than six letters and the share of one-syllable words. The result roughly matches a school grade, from 4 (very easy) to 15 (very hard).
How exact are the results?
The formulas are exact; the syllable count is not. The check counts syllables with a rule of thumb (vowel groups, common diphthongs, some exceptions) and no dictionary, so single words can be off by one. Over a longer text the errors mostly even out. Treat the score as a guide.
Is my text sent anywhere?
No. All calculations run in your browser. The text is not sent to a server and not stored.
Sources
- Wikipedia (German): Lesbarkeitsindex
- Wikipedia: Flesch–Kincaid readability tests
- Flesch, R. (1948): A new readability yardstick. Journal of Applied Psychology 32(3), 221–233
- Amstad, T. (1978): Wie verständlich sind unsere Zeitungen? Doctoral thesis, University of Zurich
- Bamberger, R. & Vanecek, E. (1984): Lesen – Verstehen – Lernen – Schreiben. Vienna: Jugend und Volk