Formulas for the readability assessments
| Readability Assessment | Variables | Algorithm |
|---|---|---|
| Coleman-Liau Index | L, average number of letters per 100 words | (0.0588 × L) − (0.296 × S) − 15.8 |
| S, average number of sentences per 100 words | ||
| Flesch Reading Ease | B, average number of syllables | 206.835 − (84.6 × [B/W]) − (1.015 × [W/S]) |
| W, average number of words per sentence | ||
| S, average number of sentences | ||
| Flesch-Kincaid Grade Level | SY, average number of syllables per word | (0.39 × W) + (11.8 × SY) − 15.59 |
| W, average number of words per sentence | ||
| FORCAST Formula | SS, number of single-syllable words in a 150-word sample | 20 − (SS/10) |
| Fry Graph | Average number of sentences and syllables per 100 words | 1) Extract a 100-word passage |
| 2) Count the number of sentences, counting half a sentence as 0.5 | ||
| 3) Count the number of syllables | ||
| 4) Find the point on the chart | ||
| (3 samples recommended) | ||
| Gunning Fog Index | S, number of sentences | 0.4 × [W/S + ([C/W] × 100)] |
| W, number of words | ||
| C, number of words with ≥3 syllables | ||
| New Dale-Chall | AW, average number of words per sentence | (0.1579 × U) + (0.0496 × AW) |
| U, percentage of unfamiliar words | ||
| New Fog Count | C, number of complex words | ([(E + [3 × C])/S] − 3)/2 |
| E, number of easy words | ||
| S, number of sentences | ||
| Raygor Readability Estimate | Average number of sentences | 1) Extract a 100-word passage |
| Long words (≥3 characters) per 100 words | 2) Count the number of sentences, estimated to the nearest 10th | |
| 3) Count the number of words that are ≥6 letters | ||
| 4) Find the point on the chart | ||
| (3 samples recommended) | ||
| SMOG | C, average number of words with ±3 syllables | 1.043 × √([C × (30/S)] + 3.1292) |
| S, average number of sentences |