Lexile Score Calculator Formula

Understand the math behind the lexile score calculator. Each variable explained with a worked example.

Use the Lexile Score Calculator

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 / 10

Variables

VariableDescriptionDefault
avg_sentence_lenAverage Sentence Length (words)15
avg_word_freqMean Log Word Frequency3.5

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.

avg_sentence_len = 15avg_word_freq = 3.5
  1. 01Lexile = round(200 x 15/10 - 100 x 3.5 + 800)
  2. 02= round(300 - 350 + 800) = round(750) = 750L
  3. 03Approximate grade level = round(750 / 100) = 8

Ready to run the numbers?

Open Lexile Score Calculator