Channel Strategy & Niche
Total Addressable Market
Also called: TAM, addressable audience, market size
TAM is the ceiling. For a channel it means everyone with the interest you serve, in the languages you publish in, before you subtract the ones already watching somebody else. Estimating it heads off two mistakes: picking a niche too small to support the channel you want, and assuming a huge niche will be easy because it is huge.
Rough numbers beat none. Search volumes, the subscriber counts of the biggest channels in the space and the size of the equivalent forum or subreddit will bracket it well enough to decide. A niche whose largest channel has 40,000 subscribers is telling you something.