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Communicative Development Inventories (CDIs) are tools for measuring vocabulary size and growth. We make use of parents' extensive experience with their own child to estimate vocabulary skills.

Filling out the Oxford CDI © Oxford University Images/Nasir Hamid
Filling out the Oxford CDI

Oxford CDI Studies

Communicative Development Inventories (CDIs) are tools for measuring vocabulary size and growth. These vocabulary 'checklists' have a long history in the study of language development. CDI studies at the Oxford University BabyLab employ a UK CDI to measure standardized vocabulary score in the local UK population, and to model growth as a function of age (see below). You can try out the Online CDI Tool to find out how many of our standard test-words your child understands. An alternative approach uses statistical modelling to estimate the possible size of a toddler's total vocabulary, based on a CDI score. You can try out the online Vocabulary Size Estimator.

The Oxford Communicative Development Inventory (OCDI)

This checklist of words is a tool for assessing the development of receptive and productive vocabulary through parental report. We typically use it with children aged from about 11 to 26 months.

The Oxford CDI has been used in the UK since 1998. It contains 416 standard words, for which both comprehension and production are assessed. The eight-page OCDI form is available for download. Alternatively, you can try out the Oxford CDI Online, for a quick summary of how many words your child knows or says.

Also available for download is a OCDI database containing (anonymous) results for several hundred children. The OCDI Database currently contains responses for 547 children aged 9.5-27.2 months. The OCDI Database is downloadable in three separate files.

A summary of these data is given below, in the graphs showing vocabulary size by age. The graphs show how the number of words produced and understood by children changes as a function of children's age. These graphs were generated from the OCDI Database by taking a moving average across 20 children.


If you use the Oxford CDI form, the Oxford CDI Online or the Oxford CDI database available from this website, please cite:

Hamilton, A., Plunkett, K., & Schafer, G., (2000). Infant vocabulary development assessed with a British Communicative Development Inventory: Lower scores in the UK than the USA. Journal of Child Language, 27, 689-705. (Abstract)


  • The Oxford CDI Form: pdf
  • The Oxford CDI Form extended: pdf
  • The Oxford CDI 100 words shortened format: pdf
  • The Oxford CDI Database: Tab-delimited files Part 1Part 2Part 3