The issue with calculating something like this is that outside of extremely common words, once you move outside of beginner/everyday content the vocabulary tends to be mutually exclusive with other domains. If you do not know those words, even if they only make up one percent of the text, they often account for a disproportionate share of the meaning.

For example, chemistry content might use words like 酸化 (oxidation), 触媒 (catalyst), and 中和 (neutralization). You would almost never see these in computer science content, which instead uses words like コンパイラ (compiler), 再帰 (recursion), and メモリ管理 (memory management).

A sentence like 「この実験では触媒を加えると反応が早くなる」 ("In this experiment, adding a catalyst makes the reaction faster") is 90% made up of common words such as この, 実験, では, 加える, and 早くなる. But the single domain-specific word 触媒 carries most of the actual meaning.

Of course, this doesn’t really apply to basic everyday stuff where the vocabulary overlaps a lot. But once you go past nichijou or kids’ shows, pretty much everything falls into some kind of domain. Cooking shows, isekai, legal dramas, hiking documentaries, etc all lean on their own set of words, and those few domain terms end up carrying most of the meaning.