Lexile Score Calculator Formula
Understand the math behind the lexile score calculator. Each variable explained with a worked example.
Formulas Used
Estimated Lexile Score
lexile = round(200 * avg_sentence_len / 10 - 100 * avg_word_freq + 800)Approximate Grade Level
grade_est = round((200 * avg_sentence_len / 10 - 100 * avg_word_freq + 800) / 100)Sentence Complexity Factor
difficulty = avg_sentence_len / 10Variables
| Variable | Description | Default |
|---|---|---|
avg_sentence_len | Average Sentence Length (words) | 15 |
avg_word_freq | Mean Log Word Frequency | 3.5 |
How It Works
How to Estimate a Lexile Score
Lexile measures are based on sentence length (syntactic complexity) and word frequency (semantic difficulty).
Simplified Formula
Lexile ≈ 200 x (ASL / 10) - 100 x MLWF + 800
Where ASL = Average Sentence Length and MLWF = Mean Log Word Frequency.
Higher Lexile scores indicate more difficult text. Typical range: 200L (early reader) to 1600L (advanced).
Worked Example
A text has average sentence length 15 and mean log word frequency 3.5.
- 01Lexile = round(200 x 15/10 - 100 x 3.5 + 800)
- 02= round(300 - 350 + 800) = round(750) = 750L
- 03Approximate grade level = round(750 / 100) = 8
Frequently Asked Questions
What is a good Lexile score for my child?
It depends on age. Grade 3: 520–820L, Grade 6: 925–1070L, Grade 9: 1050–1260L. Match books to your child's measured Lexile.
How is Lexile different from grade level?
Lexile is more precise and text-specific. Grade level is a general estimate, while Lexile allows matching a reader to specific books.
Can adults have Lexile scores?
Yes, adult readers typically range from 1000L to 1400L. Professional and academic texts can exceed 1400L.
Ready to run the numbers?
Open Lexile Score Calculator