What are the exact levels when each tier of spell books becomes available

the-elder-scrolls-v-skyrim

When googling this question, I only found forum arguments about this as well as approximate guesses.

So I'm now looking for more accurate answer: At which level of each magic skill do spell books of each tier become available at their respective merchants?

Best Answer

To quote UESP:

Most spell tomes can be purchased from merchants. Novice- and apprentice-level spell tomes can be purchased from the regular spell vendors found in each of Skyrim's cities. Also, adept- and expert-level spell tomes only appear in the mage's merchandise when your magic skill is high enough (40 for Adept and 65 for Expert spells). After reaching the required skill level, you must wait for the mage's merchandise to be reset (typically two days in-game), or, save, then attack the merchant and reload, before the new tomes will appear. Master-level spell tomes can only be acquired once that school's ritual spell quest has been completed.