The Area Level determines the item level of Gear that drops. The item level attached to gear determines what modifiers can roll on the item and the tiers of those modifiers. Plainly said, the higher your area level the more powerful items you will find.
The Area Level also determines the type of gear you will see. For example, early game items such as Wooden Swords become much more rare once you are far into the late game, but they can still drop.
The Overworld uses progression-based area levels. Boss Domains and Explorable Maps use the area level assigned by their map item.
The Overworld starts at Area Level 1. Defeating each listed progression boss raises the Overworld to the corresponding Area Level. The Eater of Worlds and Brain of Cthulhu share the same milestone, entering Hardmode raises the level to 35, and the Overworld caps at Area Level 70 after the Lunatic Cultist. Defeating the Moon Lord does not raise the cap further.
| Progression | Area Level |
|---|---|
| (DEFAULT) | 1 |
| King Slime defeated | 5 |
| Eye of Cthulhu defeated | 10 |
| Eater of Worlds or Brain of Cthulhu defeated | 15 |
| Queen Bee defeated | 20 |
| Deerclops defeated | 25 |
| Skeletron defeated | 30 |
| Hardmode / Wall of Flesh defeated | 35 |
| Queen Slime defeated | 40 |
| The Twins defeated | 45 |
| The Destroyer defeated | 50 |
| Skeletron Prime defeated | 55 |
| Plantera defeated | 60 |
| Golem defeated | 65 |
| Lunatic Cultist defeated | 70 |
| Moon Lord defeated | 70 (cap) |
| Domain | Area Level |
|---|---|
| King Slime | 5 |
| Eye of Cthulhu | 10 |
| Eater of Worlds | 15 |
| Brain of Cthulhu | 15 |
| Queen Bee | 20 |
| Deerclops | 25 |
| Skeletron | 30 |
| Wall of Flesh | 35 |
| Queen Slime | 40 |
| The Twins | 45 |
| The Destroyer | 50 |
| Skeletron Prime | 55 |
| Plantera | 60 |
| Golem | 65 |
| Duke Fishron | 65 |
| Empress of Light | 70 |
| Lunatic Cultist | 70 |
| Moon Lord | 70 |
Explorable Map area level is calculated as 70 + Tier. Tier 1 maps start one level above the Overworld cap, and each tier adds one level up to Tier 11.
| Tier | Area Level |
|---|---|
| 1 | 71 |
| 2 | 72 |
| 3 | 73 |
| 4 | 74 |
| 5 | 75 |
| 6 | 76 |
| 7 | 77 |
| 8 | 78 |
| 9 | 79 |
| 10 | 80 |
| 11 | 81 |