How does GPT-4 calculate page length?

I’m building a custom GPT that analyzes user-uploaded documents. One aspect of this analysis involves calculating the document’s page length. I’ve been attempting to do this through GPT instructions, but I’ve noticed the model often hallucinates the page length (e.g., predicting 5 pages for a 1-page document).
I’m wondering if GPT-4 is inherently capable of performing this task, and if not, I would appreciate any suggestions on alternative methods to accurately determine page lengths.

Got this response from GPT-4 itself:

Don’t know if it is hallucinating, could someone from OpenAI team pls confirm?