The German Wiener Sachtextformel tool computes the WSTF — the de facto standard readability index for German non-fiction. Unlike English formulas, it is calibrated on German texts, so it handles German’s long compound words correctly. The output is a number that maps to the German school grade a reader needs to understand the passage.
Why German needs its own readability formula
English formulas like the Flesch Reading Ease or the Fog Index are calibrated on English word and sentence statistics. German poses two specific challenges that make direct application of these formulas misleading:
- Compound words: German builds complex ideas into single words — “Kraftfahrzeughaftpflichtversicherung” (motor vehicle liability insurance) is one word with many syllables. English formulas treat long words as a readability penalty, but a single German compound might carry the semantic weight of an entire English phrase.
- Sentence length: German academic and legal prose traditionally uses long, heavily subordinated sentences with multiple embedded clauses, which would massively inflate English readability penalties.
The Wiener Sachtextformel was developed specifically on a corpus of German non-fiction texts and calibrated so that the output grades align with German school-reading expectations.
How it works
The tool tokenises your text into sentences and words, counts syllables per word, and computes four predictors as percentages of the total word count (except sentence length):
- MS — percentage of words with 3 or more syllables.
- SL — average sentence length (words ÷ sentences).
- IW — percentage of words with more than six letters.
- ES — percentage of words with exactly one syllable.
It then applies the first Wiener Sachtextformel:
WSTF = 0.1935·MS + 0.1672·SL + 0.1297·IW − 0.0327·ES − 0.875Syllables are counted by the vowel-nucleus method (each maximal vowel run = one syllable), the same approach used by the German Syllable Counter.
Interpreting the score — a practical grade guide
| WSTF score | Approximate level | Example text types |
|---|---|---|
| 4–5 | Primary school | Children’s books, simple instructions |
| 6–7 | Lower secondary | General news articles, popular science |
| 8–9 | Upper secondary | Quality newspapers, standard business writing |
| 10–11 | University entry | Specialist magazines, professional reports |
| 12–13 | University level | Academic papers, technical documentation |
| 14–15 | Advanced specialist | Legal texts, medical journals |
For broad public communication — website copy, citizen information, public health notices — aim below 7. German plain-language standards (Leichte Sprache, Einfache Sprache) target scores around 4 to 6.
Worked example
Consider two versions of the same sentence:
Version A (complex): “Die Inanspruchnahme der im Rahmen des Sozialgesetzbuchs vorgesehenen Leistungsansprüche setzt die vorherige Antragstellung beim zuständigen Leistungsträger voraus.” (WSTF might score around 14–15)
Version B (plain): “Um Sozialleistungen zu erhalten, müssen Sie zuerst einen Antrag stellen.” (WSTF might score around 5–7)
Both say “To receive social benefits, you must first submit an application.” The WSTF score drops sharply when compound words are split and sentence structure is simplified.
Practical uses
- Content writers and editors use the WSTF to benchmark drafts against target audiences. Government agencies and public-sector communicators in Germany increasingly set explicit readability targets.
- UX writers optimising German-language interfaces can paste button labels, tooltips, and error messages to check they do not exceed secondary-school reading level.
- Translators working from English into German can check whether their German output has drifted into a more complex register than the source.
- Researchers in linguistics and communication use the WSTF as a standard metric when comparing corpora of German texts.
Limitations to keep in mind
Scores are most reliable on passages of at least a few sentences; very short inputs make SL and the percentages unstable. The formula treats abbreviations and numerals loosely — a passage full of dates, percentages, and codes will have its word-length statistics skewed. The WSTF measures surface-level linguistic complexity, not conceptual difficulty; a text with short sentences and simple vocabulary can still be hard to understand if the topic is complex and assumes background knowledge.