Flesch–Kincaid Grade Level

In plain English

A grade of 8 means the text suits a reader in their eighth year of US schooling, roughly thirteen years old. A grade of 16 means a university graduate.

It uses exactly the same two counts as Flesch Reading Ease — sentence length and syllables per word — but combines them differently and outputs a year rather than a 0–100 score.

A worked example

The formula is 0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59, on the same sentence used for Reading Ease.

Sentence: "The committee reached a decision about the proposal."

words / sentences   = 8
syllables / words   = 13 ÷ 8 = 1.625

0.39 × 8   =  3.12
11.8 × 1.625 = 19.18
3.12 + 19.18 − 15.59
             = 6.7

Grade 6.7 — a competent eleven-year-old. The same sentence scored 61.2 on Reading Ease, which is the plain-English band, so the two formulas agree here.

They do not always agree, because the weightings differ. Grade Level is more sensitive to sentence length relative to syllables than Reading Ease is, so a long sentence of short words separates them.

The grade is not a hard ceiling. It is a rough correspondence built decades ago on US Navy training material, and it does not know your reader's subject knowledge — the single largest factor in whether they will follow you.

Why it matters for AI detection

It is the readability figure most institutions and style guides actually specify, usually as a maximum, which makes it the one people are asked to hit.

Hitting it badly is easy. Splitting every sentence at the conjunction lowers the grade and damages the prose, and the number will happily reward you for it.

As with every readability measure, it has no relationship to AI detection. Writing at a lower grade level does not make text look more or less machine-generated, and treating it as a lever on a detection score is a misunderstanding of what both numbers measure.

Commonly confused with

Flesch Reading Ease

The older of the two and the inverse in direction. High Reading Ease means easy text; high Grade Level means hard text. Quoting one as the other reverses the meaning entirely.

Reading age

Reading age is expressed in years of a reader's life; grade level is expressed in years of US schooling. They are offset by about five and are not interchangeable outside the US.

Read next

• Readability checker
• Flesch Reading Ease
• Readability