1-4: 9-B (
Scales to Burning Hands)
5-8: 9-A+
(Scales to Conjure Barrage)
9-10: 8-C
(Scales to Cone of Cold)
11-12: At least High 8-C, likely 8-B, possibly 8-A
(Has a lot of spells in these areas of power)
13-17 (Assuming 5th Edition*): Low 7-B+
(Scales to Legendary Dragons)
18-24: 6-C+
(Scales to Imix and the Elemental Princes)
25-33: At least Low 6-B+, possibly 6-B
(Scales to Father Llymic and the Elder Evils)
34-56: High 6-A
(Scales to the Phaethon)
57+: At least High 6-A, likely 2-C, possibly 2-A
(Scales to Hecatoncheires)
*- If you're using 3rd edition level/CR scaling, Low 7-B goes up to CR 19, and CR 20-24 is 6-C.
There are exceptions to this tier list based on factors outside of player level- for example, being the Chosen of a Deity makes you effectively a higher level despite not actually being a higher level. Similar divine ranks up to demigod improve your overall AP outside of your level. Some players abandon player levels and outright ascend to godhood (or, in the case of Mystara, Immortality) becoming Tier 2 (Tier 1 if in Mystara- or Low 1-C, more specifically). Thus the above scale is a general one and does not account for abnormalities.