ATOS Level and Lexile Measure – What does it mean?

Have you noticed that when you take out certain books, an ATOS level or a Lexile measure is given? Both are measures of the difficulty and readability of a book. These measures guide you in recommending books that are on your child’s reading level. Keep in mind that children often like to read easier books purely for enjoyment.

The ATOS level is based on a readability formula. It considers the number of words per sentence and the difficulty of the words used.

The Lexile measure is based mainly on the length of sentences and how often words repeat.

Both measures give little indication of whether these books will pique your child’s interest or not. For this reason, an interest level is also often given. So, why are these measures important? It’s all well and good for you to cultivate your child’s love of reading by giving him/her easy books to read. However, for your child’s reading ability to improve, he/she must read books that have challenging vocabulary and complex plots.

Below is a basic guide for navigating these reading levels:

Age Grade ATOS level Lexile measure
up to 6 years up to 0.9 up to 199
7 years 1 1.0-1.9 200-299
8 years 2 2.0-2.9 300-399
9 years 3 3.0-3.9 500-799
10 years 4 4.0-4.9 600-899
11 years 5 5.0-5.9 700-999
12 years 6 6.0-6.9 800+


Here are some of our popular books and the ATOS levels of each:

Jeremy Strong3.1

Novel Title Author ATOS
Magic Treehouse series Mary Pope Osbourne 2.6
Judy Moody series Megan McDonald 3.0
My Brother’s Famous Bottom Gets Crowned!
A to Z mysteries Ron Roy 3.2
Little house series Laura Ingalls Wilder 3.5
Because of Winn-Dixie Kate DiCamillo 3.9
Boxcar series Gertrude Chandler Warner 3.9
The Gooney Bird series Lois Lowry 3.9
The Diamond Brothers series Anthony Horowitz 4.1
Charlie and the Great Glass Elevator Roald Dahl 4.4
39 Clues series Various Authors 4.5
Middle School series James Patterson 4.5
Danny the Champion of the World Roald Dahl 4.7
Henry Huggins series Beverly Cleary 4.7
Mr Stink David Walliams 4.7
The Butterfly Lion Michael Morpurgo 4.7
Double Decker Jacqueline Wilson 4.7
The Kane Chronicles series Rick Riorden 4.7
House of Robots series James Patterson 4.7
The Giraffe and the Pelly and Me Roald Dahl 4.7
The Code Busters Club series Penny Warner 4.7
Hardy Boys series Franklin W. Dixon 4.8
The Chocolate Box Girls series Cathy Cassidy 4.9
Alex Rider series Anthony Horowitz 5.1
Diary of a Wimpy Kid series Jeff Kinney 5.2
Ruby Redfort series Ruby Redfort 5.3
Nancy Drew series Carolyn Keene 5.5
The Chronicals of Narnia CS Lewis 5.7
The Black Stallion series Walter Farley 6.1