What is MLU?

What is Mean Length of Utterance (MLU)?

The term “mean length of utterance” is often used when speech therapists talk about increasing the sentence length of children. For example, if a child is learning how to talk they often have a MLU of one because they are only using one word at a time. As a child grows their MLU should increase with their age.

Speech-language pathologists measure MLU in morphemes. A morpheme is the smallest unit of language that holds its own meaning. If you separate a word into parts, each part would have its own meaning. For example, the word “banana” is one morpheme. You cannot divide the word into smaller words with meaning. If you add an “s” to the end you get “bananas”, you have two morphemes because you can divide the word into “banana” (meaning the yellow fruit) and “s” (meaning more than one). Another word that has two morphemes is “smelling.” The word could be divided into “smell” (the action) and “ing” (meaning it is currently happening).


Why is this important?

MLU is important because if a child says “my toy,” that’s two morphemes. If the child says “my toys” then the child used three morphemes. If you were counting by the number of words the child used, they both used two, however the child who added the “s” made the utterance more linguistically complex.

According to Brown’s Stages of Language Development a child should be developing at the following:

12-26 mos  ~  1.0 – 2.0

27-30 mos  ~  2.0 – 2.5

31-34 mos  ~  2.5 – 3.0

35-40 mos  ~  3.0 – 3.75

41-46 mos  ~  3.75 – 4.5

47 mos +  ~  4.5 +

So what can you do for your child at home?

In order to increase sentence length, you need to figure out what is missing from the child’s speech. In addition to seeing a speech therapist, several areas you could target at home include: talking to your child with new words, reading to your child, pointing out words you see, listen and respond when your child talks, increasing vocabulary, improving grammatical markers, and using expansions. An early vocabulary should include nouns, verbs, descriptors, possessives, negatives, demonstratives, and question words. If your child has limited vocabulary, working on increasing vocabulary could expand their language and ultimately increase their MLU. If your child says “go inside” you could expand on their sentence by saying “I go inside” or “Go inside, please.” When a parent provides models it allows the child to see how they could expand on their language. If your child does not have the appropriate mean length of utterance for their age, considering seeing a speech language pathologist (SLP). SLPs can help children with language disorders. Good language skills can create a foundation for learning, behavior, self-esteem, and social skills.

For more information please refer to the links below.

Kimberly Chirco MA CF-SLP, TSSLD


Bowen, C. (1998). Brown’s Stages of Syntactic and Morphological Development. Retrieved from http://www.speech-language-therapy.com/index.php?option=com_content&view=article&id=33 on

Clark, C., CCC-SLP. (n.d.). Increasing Sentence Length (MLU) – Speech and Language Kids. https://www.speechandlanguagekids.com/increasing-sentence-length-mlu/

Preschool Language Disorders – asha.org. (n.d.). http://www.asha.org/public/speech/disorders/Preschool-Language-Disorders/




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