What Is Character Error Rate (CER)?

Direct definition

Character error rate (CER) is the same edit-distance idea as WER, computed on characters instead of words. It is common for languages without clear word boundaries and as a complement to WER.

The sections below explain how character error rate is used in transcription and subtitle work, what people often mix up, and which VideoText workflow applies when the next step is a file or review pass.

Key takeaways

• CER = (S + D + I) / number of reference characters.
• A low WER can hide character-level mess in punctuation or morphology.
• Do not convert CER to “percent accurate” without stating the metric.

When CER is preferred

Mandarin and other scripts are often scored with CER. Some punctuation studies also report CER because a period is a character, not a word.

Related terms

• word error rate
• transcription accuracy
• All glossary terms

Sources

1. OpenAI: Whisper paper (evaluation / normalizer context)