Measure how readable your Spanish text is
English readability formulas like Flesch were calibrated for English and systematically misjudge Spanish, whose words carry more syllables on average. The INFLESZ scale solves this by using the Fernández-Huerta legibility formula — calibrated specifically for Spanish — and mapping its 0-100 output onto five plain-language difficulty bands. It is the go-to standard for Spanish health services checking that patient leaflets, consent forms, and health education materials are actually readable.
The formula and its inputs
The tool tokenises your text into words and sentences, then estimates syllables by counting vowel groups while respecting Spanish diphthong and hiatus rules. From those counts it derives two inputs:
- P — average number of syllables per 100 words (a measure of word complexity)
- F — average number of words per sentence (a measure of syntactic complexity)
The INFLESZ score is then:
INFLESZ = 206.84 − (0.60 × P) − (1.02 × F)A higher score means shorter words and shorter sentences and therefore easier reading. The result is clamped to 0–100.
The five INFLESZ bands
| Score range | Band | Interpretation |
|---|---|---|
| Above 80 | Very easy | Children’s text, casual health tips |
| 65 to 80 | Fairly easy | General public material, patient leaflets |
| 55 to 65 | Normal | Standard press, general information |
| 40 to 55 | Somewhat difficult | Technical or scientific writing |
| Below 40 | Very difficult | Academic, legal, or highly specialised text |
Spanish health authorities and patient-rights organisations recommend that material intended for the general public reach at least the normal band (55–65) and that patient-facing documents — informed consent forms, discharge instructions, medication leaflets — reach the fairly easy band (65–80) or higher.
Why INFLESZ rather than Flesch?
The Flesch Reading Ease formula, adapted for English, uses constants derived from English word and sentence statistics. Spanish words are phonologically richer — verbs conjugate into multi-syllable forms, noun phrases carry adjective agreement, and derivational morphology produces longer words — so a naive port of the English formula produces scores that are consistently too low. Fernández-Huerta adapted the coefficients for Spanish text, and INFLESZ applies that adapted formula with Spanish-relevant band labels.
How to improve a low score
The two highest-leverage levers are sentence length and word complexity:
- Sentence length: a 30-word sentence pushes F sharply upward. Breaking it into two 15-word sentences raises the score by several points without changing the meaning.
- Word complexity: replacing a four-syllable clinical term (hemorragia) with a two-syllable everyday word (sangrado) lowers P measurably. Spanish medical style is often criticised for using Latinate terms when plain equivalents exist.
- One idea per sentence: dependent clauses with relative pronouns (el cual, cuyo) extend sentences and add syntactic load that scores poorly on any readability formula.
Aim for at least the normal band (55–65) for general audiences, and the fairly easy band (65–80) for patient-facing or learner material. Very easy scores (above 80) are appropriate for younger readers, health apps, or step-by-step instructions.
A worked scenario
A patient information leaflet that currently scores 47 (somewhat difficult) is likely using long sentences — perhaps averaging 22 words — and clinical vocabulary averaging close to three syllables per word. Editing the same content to 14-word average sentences and substituting everyday words typically pushes the score toward the normal or fairly easy range without losing accuracy.