SLPcentralFree MLU Calculator
for SLPs
Paste a language sample, one utterance per line. You get MLU in words and in morphemes, total and different words, and maze percentage, with every utterance’s count there to check and change.
Your sample never leaves your browser. It isn’t sent to SLPcentral or anyone else, it isn’t saved, and it’s gone when you reload or close this page.
Don’t paste names or identifying details.
Put mazes in (parentheses) and write X for an unintelligible word. Lines starting with E: (or any label other than C:) are skipped.
We turn off the browser’s spell-check and ask it not to translate this tool. Add-ons you’ve installed (like grammar checkers) can still read any page you open.
Paste a sample above, or try the practice sample, to see MLU and the counts.
Brown’s rules, as commonly taught.
- One morpheme added for each ending: plural -s (dogs), possessive ’s (Mom’s), 3rd person -s (runs), regular past -ed (jumped) and progressive -ing (running).
- Contractions count as two: can’t, I’ll, we’re, it’s, I’m. Turn on the option to count can’t, don’t and won’t as one, for a young child who doesn’t yet say can, do or will on their own.
- One morpheme: irregular past (went) and plurals (feet), compound words (birthday, choo-choo), names, diminutives (doggie), catenatives (gonna, wanna, hafta, gotta) and auxiliaries (is, can, will). Join a two-word name with an underscore (Mickey_Mouse).
- Not counted: mazes you put in (parentheses), fillers (um, uh, er, oh), part-words (wa-) and repeated words, which count once. If a repetition was for emphasis (no, no, no), raise that line’s count.
- Unintelligible: type X, XX or XXX for a word you couldn’t understand. That whole utterance is left out of every count, because Brown used fully transcribed utterances.
- Labels and codes: lines starting with E: (examiner) or any other speaker label (SLP:, Mom:) are skipped, and C: (child) labels are removed. Unlabeled lines count as the child’s. [Codes] and {comments} are ignored. Words you already marked SALT-style (dog/s) count as you marked them.
- Good to know: a capitalized word inside a sentence is read as a name. Overregularized forms like goed count the -ed. Words ending in -ing or -ed count the ending even when they work as adjectives or nouns (scared, excited, a building, a drawing), so check those, along with used to and supposed to. Different words (NDW) counts root words, so dog and dogs count once.
Automatic counts are an estimate from spelling. Check each utterance and change any count the tool got wrong; the totals update as you go.
How to collect a language sample.
Get the child talking
Use play or conversation about something they care about, with open prompts (“Tell me about…”, “What happened next?”) instead of yes/no questions. Follow your district’s rules if you record it.
Aim for 50 to 100 utterances
Brown (1973) used 100 utterances. Many clinicians collect 50 to 100 in a row. A smaller sample still helps, but its MLU moves more from one sample to the next.
Transcribe one utterance per line
Break utterances at pauses, a falling voice or a complete thought. Put mazes (false starts, revisions) in parentheses and write X for a word you couldn’t understand.
Paste, check, then interpret
Look over the table, fix any count, and compare the result with your preferred norms alongside the rest of your assessment.
How MLU is calculated.
MLU in morphemes = total morphemes ÷ number of utterances
MLU in words = total words ÷ number of utterances
| Utterance | Words | Morphemes |
|---|---|---|
| the dog/s ran | 3 | 4 |
| he jump/ed | 2 | 3 |
| she want/s it | 3 | 4 |
11 morphemes ÷ 3 utterances = MLU 3.67 in morphemes; 8 words ÷ 3 = 2.67 in words.
MLU calculator FAQ.
How do you calculate MLU?
Count the morphemes in each utterance, add them up, and divide by the number of utterances. MLU in words works the same way with words. For example, 230 morphemes across 50 utterances is an MLU of 4.6.
How many utterances do I need?
Brown (1973) used 100 utterances, and many clinicians collect 50 to 100 from play or conversation. A smaller sample can still be useful, but the MLU changes more from one sample to the next, so the calculator points out samples under 50.
How accurate are the automatic counts?
They apply Brown’s rules from spelling, so treat them as an estimate to check. The tool can’t hear the child: it can read a name as a plural or miss a word that was said differently from how it’s spelled. Check the table and change any utterance’s count; the totals update.
Is my language sample saved or sent anywhere?
No. The calculator runs in your browser. What you paste isn’t sent to SLPcentral or anyone else, isn’t saved, and is gone when you reload or close the page. Even so, don’t paste names or identifying details.
What MLU is typical for a child’s age?
This tool doesn’t show age norms. Compare with your preferred norms or the reference your district uses, and read the number alongside the rest of your assessment.
Counted the MLU?
Let Ollie draft the note.
In SLPcentral you log session data as you go. Mention your MLU in a Brain Dump after the session and Ollie can include it in the note it drafts, for you to check and edit.
