AI engineering glossary · Evaluation metrics
What is BPB (bits per byte)?
Bits per byte (also called bits per character, BPB): A language-model quality measure that converts the model's total negative log-likelihood, in base 2, into bits divided by the number of raw bytes or characters in the text. Because the divisor is fixed by the text, not by the tokeniser, it allows fair comparison between models that split text differently.
Bits per byte: an example
Two models with different vocabularies cannot be compared by per-token perplexity, but both can report bits per byte on the same 1 MB of text.
Related terms
More Evaluation metrics terms
Where you learn it
Bits per byte is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.