Coleman-Liau Index calculator

Paste your text to get its Coleman-Liau Index — a US grade level based on letters per word and words per sentence — with the working shown. Because it doesn’t guess at syllables, it’s one of the most consistent readability scores. Free and private to your browser.

Your text

Checked in your browser — your text isn’t sent anywhere or saved.

Paste or type some text to see its readability scores.

The Coleman-Liau Index formula

CLI = 0.0588 × L − 0.296 × S − 15.8

L — average number of letters per 100 words.
S — average number of sentences per 100 words — more sentences means shorter ones, which lowers the grade.
The result — a US school grade. Add five for a rough reading age.

Worked example

Here is the Coleman-Liau Index worked through for our sample bedtime story — press Try a sample story above to load it. It’s a short tale about an owl who can’t sleep, and it counts up like this:

Words: 118
Sentences: 18
Letters: 480

0.0588 × (480 ÷ 118 × 100) − 0.296 × (18 ÷ 118 × 100) − 15.8 = 3.6

So the story scores 3.6 — Grade 4 · ages 9–10.

What your score means

Score	Level	Who reads it easily
1 or below	Kindergarten–1st grade	Ages 5–7 · picture books, first readers
2–3	2nd–3rd grade	Ages 7–9 · early chapter books
4–5	4th–5th grade	Ages 9–11 · confident young readers
6–8	Middle school	Ages 11–14 · most adults read this comfortably
9–12	High school	Ages 14–18 · news features, business writing
13–16	College	Academic and specialist writing
17+	Graduate	Dense professional or scientific prose

What is a good Coleman-Liau score?

For a general audience, aim for grade 8 or below, the same as other grade-level formulas. For children’s books, match the grade to the reader — or a grade or two above if you’ll be reading it aloud.

Coleman-Liau leans on word length, so text with lots of long but familiar words — “everybody”, “grandmother”, “chocolate” — can score a little higher than it feels.

Where it comes from

Meri Coleman and T. L. Liau published the index in 1975 in the Journal of Applied Psychology. They wanted a formula a machine could apply to scanned text, and counting syllables was hard to automate reliably at the time — counting letters wasn’t.

That design choice still pays off: letters and sentences are unambiguous, so Coleman-Liau scores tend to agree closely between tools where syllable-based scores drift apart.

Limitations

Letters are only a proxy for difficulty. A long, common word like “understanding” counts against the text while a short, rare one like “ort” doesn’t.

Like every readability formula, it ignores meaning, structure, and the reader’s background knowledge — a clear explanation of a hard idea and a muddled explanation of an easy one can score the same.

How to calculate the Coleman-Liau Index by hand

Take a passage of at least 100 words. Count the words, the sentences, and the letters — letters only, leaving out digits, spaces and punctuation.

Work out L by dividing letters by words and multiplying by 100. Work out S by dividing sentences by words and multiplying by 100. Both are rates per 100 words, so a 250-word passage and a 90-word one can be compared directly.

Put them into the formula: multiply L by 0.0588, subtract 0.296 times S, then subtract 15.8. Round to one decimal place and read the result as a US grade.

A quick sense check: everyday English averages about 4.5 letters a word, so L sits near 450 for most prose. Separately, each extra sentence per 100 words knocks about 0.3 off the grade.

Coleman-Liau vs the Automated Readability Index

Coleman-Liau and the Automated Readability Index are the two character-counting formulas — neither needs a syllable count. ARI counts letters and digits, and adds half a grade for every extra word per sentence. Coleman-Liau counts letters only, and measures sentence length as sentences per 100 words.

On short, simple text the two can land a couple of grades apart: our sample bedtime story scores 3.6 on Coleman-Liau and 1.0 on ARI from exactly the same letter count. Neither is wrong — they were calibrated against different reading tests — so compare a text against itself on one formula, rather than one formula against another.

Frequently asked questions

How is Coleman-Liau different from Flesch-Kincaid?

Both output a US grade level, but Flesch-Kincaid uses syllables per word while Coleman-Liau uses letters per word. Letters can be counted exactly, so Coleman-Liau results vary less between tools.

What do L and S mean in the Coleman-Liau formula?

L is the average number of letters per 100 words and S is the average number of sentences per 100 words.

Can the Coleman-Liau Index be negative?

Yes. Short words in short sentences — typical of books for very young children — can push the result below zero. Read that as kindergarten level or easier.

Do numbers and punctuation count as letters?

No. This calculator counts only letters for L. Numbers still count as words, and punctuation is ignored except for finding where sentences end.

Is Coleman-Liau accurate for children’s books?

It’s a reasonable guide from about grade 2 upwards. For the very youngest books, a few long names like “Grandmother Hedgehog” can lift the score more than the story deserves, so check it against the other formulas in the reading level checker.

How much text do I need for a reliable score?

At least 100 words, and ideally a few hundred. With only a handful of sentences, one long sentence or one long word shifts the result noticeably.