It's true that most of Star Trek uses vague or made-up terms for computing measures, but Data formally refers to his own storage in units of "quadrillion bits",

It's true that most of Star Trek uses vague or made-up terms for computing measures, but Data formally refers to his own storage in units of "quadrillion bits", and apparently using that as a definition of "quad" makes for a reasonable order-of-magnitude estimate for other uses, even today.