Character Error RateCER
Definition
A metric that measures transcription accuracy at the character level rather than the word level.
Character Error Rate is the character-level equivalent of Word Error Rate, computed as (Character Substitutions + Insertions + Deletions) / Total Reference Characters. CER is particularly useful for evaluating ASR in languages without clear word boundaries (like Chinese or Japanese) and for assessing partial correctness — a word with one wrong letter contributes less to CER than to WER.
CER is generally lower than WER for the same transcript because a single word error might involve only one or two character errors. CER is commonly reported alongside WER to give a more nuanced picture of ASR accuracy.