Morpheme Counter Calculator
Calculate Mean Length of Utterance (MLU), free-to-bound morpheme ratio, morpheme density, and Brown's Stage for language development assessment.
About this calculator
This calculator computes Mean Length of Utterance (MLU) — the standard child language development metric, calculated as Total Morphemes divided by Total Utterances in a transcribed sample — and places the result into a developmental stage using Roger Brown's widely-used MLU-stage framework: Stage I below 2.0, rising through Stage II, III, and IV, up to Stage V at 3.75 and above (Brown's original scheme further splits above 4.5 into "Stage V+", but this calculator reports both as a single Stage 5). MLU responds only to Total Morphemes and Total Utterances — Free Morphemes and Bound Morphemes, which you also enter, do not factor into the MLU or Brown's Stage calculation at all. Instead they feed a separate Free-to-Bound Ratio, which describes how much of the sample's morpheme count comes from standalone words versus attached grammatical endings, independent of overall utterance length.
One thing to know before reading the Morpheme Density output: in this calculator it is computed with the exact same formula as MLU (Total Morphemes / Total Utterances), so the two figures will always match. Density is included as a separate output for readers who want a morphemes-per-utterance framing distinct from the "MLU" clinical label, not because it measures something MLU doesn't already capture here. This tool expects you to have already segmented and counted morphemes from a real transcribed sample; it does not perform morphological segmentation itself.
Inputs
Results
Mean Length of Utterance (MLU)
3
How to Use This Calculator
- Enter Total Morphemes and Total Utterances counted from your language sample (a standard sample is 50-100 utterances).
- Enter Free Morphemes (standalone words) and Bound Morphemes (attached affixes like -s or -ed) from the same sample.
- Review the Mean Length of Utterance (MLU) — the key measure of language development.
- Check the Free-to-Bound Ratio and Brown's Stage to place the sample in a developmental context.
- Use MLU and Brown's Stage together to track progress across repeated samples of the same speaker over time.
How the result changes with Total Utterances
| Total Utterances | Mean Length of Utterance (MLU) |
|---|---|
| 25 | 6 |
| 38 | 3.95 |
| 75 | 2 |
| 125 | 1.2 |
What each input means
- Total Morphemes
- Total count of all morphemes (free + bound) in the language sample.
- Total Utterances
- Number of complete utterances in the sample. Standard sample is 50-100 utterances.
- Free Morphemes
- Morphemes that can stand alone as words (e.g., 'cat', 'run', 'big').
- Bound Morphemes
- Morphemes attached to free morphemes (e.g., '-s', '-ed', '-ing', 'un-').
What each result means
- Mean Length of Utterance (MLU)
- Average morphemes per utterance. Key measure of language development.
- Free-to-Bound Ratio
- Ratio of free morphemes to bound morphemes.
- Morpheme Density
- Morphemes per utterance, indicating morphological complexity.
- Brown's Stage
- Language development stage based on MLU per Roger Brown's framework (Stage V and Stage V+ both collapse into this stage's top band).
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTotal Morphemes = 150, Total Utterances = 50, Free Morphemes = 100, Bound Morphemes = 50 = 4 input(s) provided
- Calculate Mean Length of UtteranceMean Length of Utterance3 = 3
- Calculate Free-to-Bound RatioFree-to-Bound Ratio2 = 2
- Calculate Morpheme DensityMorpheme Density3 = 3
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Does the split between Free and Bound Morphemes change my MLU result?
No — MLU is calculated only from Total Morphemes divided by Total Utterances. Free Morphemes and Bound Morphemes are separate inputs that feed the Free-to-Bound Ratio output instead; changing how your total morpheme count splits between free and bound forms, while keeping the total the same, leaves MLU and Brown's Stage completely unaffected.
Why are the Morpheme Density and MLU results always the same number?
In this calculator, Morpheme Density uses the identical formula as MLU — Total Morphemes divided by Total Utterances — so the two outputs will always be equal. Density is offered as an alternate framing of the same underlying figure rather than a distinct measurement, so don't expect it to diverge from MLU with the inputs this tool collects.
What does a larger sample size (more utterances) do to my results?
Adding more utterances to your sample, without a proportional increase in total morphemes, lowers MLU — since MLU is morphemes divided by utterance count, a bigger denominator on the same numerator brings the average down. This holds across the calculator's full declared utterance-count range, which is why a standard 50-100 utterance sample size is recommended for reliable, comparable MLU results.
Is Brown's Stage a precise clinical diagnosis of language development?
No — it's a widely-used research and clinical reference band based on MLU ranges from Roger Brown's original work, useful for broadly situating a sample within typical developmental progression, not a standalone diagnostic tool. A full speech-language assessment considers many additional measures alongside MLU before drawing conclusions about an individual child's language development.
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