Items in the Baldur's Gate series may be enchanted. This is not to be confused with an item being magical, and in this context, the game terminology not always follows the one used in the Advanced Dungeons & Dragons 2nd edition sourcebook publications.
Enchantment strength[]
In Baldur's Gate games, many creatures have skin, shell or magic that makes them entirely immune to weapons or ammunitions that are not strong enough. Such weapons will be unable to deal damage and unable to apply the on-hit effects they may carry. The combat logs display the message Weapon ineffective when a weapon or ammo strikes an immune target, and if it's a party member attacking, they are likely going to be vocal about it.
Whether a weapon is strong enough is quantified with the enchantment strength or level — a number between 0 and 6, with 0 sometimes referred to as non-enchanted. When landing a blow with a weapon, typically thanks to a successful attack roll, its enchantment strength is checked to decide if it's going to be enough to cause any harm to the target, or if it's going to be ineffective. For example, the famous katana Celestial Fury has no use whatsoever against a sound asleep and defenseless Fallen Solar, because it is a spiritual being that can only be harmed by weapons if they have at least enchantment level 4.
When it comes to ranged attacks, only the enchantment level of the ammunition matters: though bows, crossbows and slings do have their own enchantment level, they are typically not used to bonk the target's head but to propel ammo into it. Therefore it's the level of the arrow, bolt or bullet that counts. The only time when a launcher's enchantment strength matters is when it generates its own ammunition, like Tansheron's Bow: In that case, the launcher's enchantment value is passed on to the projectile it created. See the Bugs section for an exception to the exception.
Enchanted versus magical[]
It can be useful to keep in mind that whether or not an item is enchanted has no bearing on it being magical. A weapon or ammo can be magical and have enchantment level 0, like the Arrow of Dispelling, or it can have enchantment level 6 and be non-magical, like the summons from Summon Spirit Animal before the Druid reaches level 10.
Still, the vast majority of weapons with non-zero enchantment are actually magical, and the vast majority of weapons with enchantment zero are not.
Immunities found in game[]
The game applies enchantment and magical immunities through defensive spells or through a set of innate, permanent effects. A spell or set may target the enchantment level, the magical nature, or both at the same time. For example the immunities granted by Protection From Magical Weapons and Protection From Normal Weapons are targeted at respectively magical weapons and non-magical weapons, regardless of enchantment. On the other hand, the Mantle type of spells and most innate creature immunities actually contain two immunities: One to non-magical weapons regardless of enchantment, and one to all weapons below a certain enchantment level, whether magical or not.
See the wiki's immune to enchanted weapons category for creatures sorted by their immunity to enchantment levels, and immune to magical weapons for those immune to magical weapons and ammo.
How enchantment level is reported in-game[]
The game is not consistent about informing the player of a weapon's enchantment level, but it is very often listed in the weapon's name, for example Long Sword +3 or Bullet +4. Failing that, the item description often talks about it, but the wiki or a file explorer like Near Infinity should be the best resources. See the wiki's enchanted items category for items sorted by enchantment level, or check the infobox within a specific item's page.
All items have an enchantment value, but only weapons and ammunition matter to game mechanics. The game mostly mentions enchantment for those and for armor, shields and a few items "of protection" like the Cloak of Protection +2.
Confusion with other bonuses[]
Most enchanted weapons in game offer THAC0, damage and speed factor bonuses equivalent to their enchantment level. For example the Long Sword +3 has a level 3 enchantment and gives +3 THAC0, +3 damage and -3 speed factor bonuses, but it's not a rule, as illustrated by the Staff of the Magi. This staff has a level 5 enchantment but only +1 bonuses to THAC0 and damage — it can harm creatures immune to enchantment 0 to 4.
For armors and shields, they tend to offer an Armor Class bonus equivalent to their enchantment level, for example the enchantment level 2 Full Plate Mail +2 offers a +2 AC bonus over the enchantment level 0 Full Plate Armor. But again, it's not a rule, and armor enchantment does not actually affect gameplay. Finally, items "of protection" may offer an AC and a saving throw bonus equivalent to their enchantment level, but yet again that level is ignored by game mechanics.
Enemies that can only be hit by +3 and over weapon enchantments[]
These lists should be fairly complete, but a few enemies could be missing (such as those from the Black Pits II and SoD).
Enemies that require +3 enchantment to hit:
- Bosses, some (Balthazar, Bodhi, Demogorgon, Melissan)
- Demons, some (Balor, Demon Wraith, Pit Fiend)
- Golems, some (Adamantite, Greater Clay, Guardian, Ice, Iron)
- Planetars/Solars (except the Fallen Solar)
- Undead, some (Ancient Vampire, Greater Mummy, Slave Wraith)
Enemies that require +4 enchantment to hit:
- Aurumach Rilmani
- Fallen Solar (final ToB fight)
- Demiliches
- The Ravager
Enemy that requires +5 enchantment to hit:
- Lesser Demon Lord (Underdark)
Bugs[]
- When a ranged weapon generates its own ammunition and a separate ammo stack is selected, a bug makes it fire both at the same time. In that case, the enchantment level will be that of the separate ammo.