Table 2 Summary of readability formulae

Flesch–Kincaid reading grade level

Grade level

Part of the Kincaid Navy Personnel collection of tests. Designed for technical documents and suited to a broad array of disciplines

G = (11.8 × (B/W)) + (0.39 × (W/S))  − 15.59

Flesch–Kincaid reading ease

Index score (0–100)

Developed to assess the readability of newspapers. Best suited to assessing school textbooks and technical manuals. Standard test used by many US government agencies. Scores range from 0–100, with higher scores denoting easier readability

I = (206.835 − (84.6 × (B/W)) − (1.015 × (W/S)))

The Raygor estimate

Grade Level

Designed for most text, including literature and technical documents

Calculated using the mean number of sentences and long words (≥ 6 characters) per 100 words, which are plotted on to a RE Graph, where their intersection determines RGL

Fry

Grade level

Designed for a variety of texts including technical documents and literature, across a range of levels, from primary school level to university level

Calculated using the mean number of sentences and syllables per 100 words, which are plotted on to a Fry Graph, where their intersection determines RGL

SMOG

Grade level

Generally appropriate for secondary age (4th grade to college level) readers. Tests for 100% comprehension, whereas most formulas test for around 50–75% comprehension. Most accurate when applied to documents ≥ 30 sentences in length

G = 1.0430 × √C + 3.1291

Coleman–Liau

Grade level

Designed for secondary age (4th grade to college level) readers. Formula is based on text from the .4 to 16.3 grade level range. Applicable to numerous sectors

G = (− 27.4004 × (E/100)) + 23.06395

FORCAST

Grade level

Devised for assessing U.S. Army technical manuals and forms. It is the only test not designed for running narrative

G = 20 − (M/10)

Gunning fog

Grade level

Developed to assist American businesses improve the readability of their writing. Applicable to numerous disciplines

G = 0.4 × (W/S + ((C*/W) × 100))