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I saw in a recent answer a reference to 1/3 casters and 1/2 casters, and have never encountered this terminology before:

Paladin's are known as 1/2 casters, so their spell progression isn't as big as full casters.

What does it mean to be a 1/3 caster vs a 1/2 caster vs a full caster? How does one distinguish between the three, and which classes correspond to which types of caster?

V2Blast
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B. S. Morganstein
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3 Answers3

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"1/X Caster" is shorthand for how quickly a character gains "spellcaster levels" (and with them, more spell slots)

The progression for each of these spellcaster types looks like this, with the first column representing Character Level as a Single-classed X and the other columns representing the "Spellcaster Level" they have as that Single-classed X at a given level.

Character Level Full Half Third
1 1 - -
2 2 1 -
3 3 2 1
4 4 2 2
5 5 3 2
6 6 3 2
7 7 4 3
8 8 4 3
9 9 5 3
10 10 5 4
11 11 6 4
12 12 6 4
13 13 7 5
14 14 7 5
15 15 8 5
16 16 8 6
17 17 9 6
18 18 9 6
19 19 10 7
20 20 10 7

The classes that fall into these categories are:

Full Half Third Other
Bard Artificer* Arcane Trickster Warlock†
Cleric Paladin Artificer (Unearthed Arcana)
Druid Ranger Eldritch Knight
Sorcerer
Wizard

*The Artificer is a Half-Spellcaster, but unlike other Half Spellcasters, they gain their spellcasting feature at level 1, instead of level 2, and are treated like level 1 spellcasters at that level.
†Warlocks are unique in that their spell access resembles that of a Full Spellcaster, but their Spell Slots are completely divorced from the system that all other spellcasters use, so they need their own category.

Your spellcaster level determines how many spell slots you have, and the maximum level of spell slot that you'll have will (usually) be half your spellcasting level, rounded up.

So if you're a level 9 Paladin (Half Spellcaster), you have a Spellcaster level of 5 (See the Character Level 9 row for a Half Spellcaster). Therefore, you have spell slots equivalent to a level 5 Cleric (Full Spellcaster) and to a level 13 (or 14 or 15) Eldritch Knight (Third Spellcaster)—and for each of these characters, their Spell Slot total is:

  • 4 1st Level Slots,
  • 3 2nd Level Slots,
  • 2 3rd Level Slots.

"1/X Caster" also comes into play in the Multiclassing Rules

What kind of Spellcaster you are affects how your levels are added together when you Multiclass into multiple kinds of spellcaster.

Spell Slots. You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, half your levels (rounded down) in the paladin and ranger classes, and a third of your fighter or rogue levels (rounded down) if you have the Eldritch Knight or the Arcane Trickster feature.† Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.

—Multiclassing, Player's Handbook, pg. 164

†Artificers have a special rule: when adding their levels for multiclassing purposes, you round up after dividing by two, instead of rounding down. Note also that Warlocks are not included in this list; again, their Spellcasting is completely different from other classes, so they aren't considered in calculating a character's normal spellcasting level.

For example, suppose we have a Multiclassed Wizard 5/Eldritch Knight 11. We add their levels by first dividing them by the level of spellcaster they are, so we take 5 Wizard Levels (5 * 1/1 = 5) and 11 Eldritch Knight Levels (11 * 1/3 = 3.666 → Rounded Down to 3) and add them together to find that this character is the equivalent of a Level 8 Spellcaster, gaining 4 1st Level Slots, 3 2nd Level Slots, 3 3rd Level Slots, and 2 4th Level Slots.

Xirema
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  • One interesting thing to note is that all casters, regardless of which level they initially gain access to spells, are effectively treated as if their spellcasting progression starts at Lv.1. This is most noticeable with new artificers, but the patten (and formula) itself always uses 1 as a starting point (regardless of whether the character actually gains their Spellcasting feature at 1). – Justin Time - Reinstate Monica Jul 26 '19 at 19:40
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    Personally, I round down only at the end. This way, when combining 1/2 and 1/3 casters, it helps a little. Example, 5 Pal 5 Ranger would be 2.5 rounded to 2 + 2.5 rounded to 2, giving 4. Rounding at the end would be 2.5+2.5 giving 5.
    Combining a level 5 Pal and 5 Trickster would be 2.5 + 1.66=4.1 or 4, rather than the 3 when rounding before adding. RAW seems to round down then add to punish multiclass further.     – MikeP Jul 26 '19 at 20:58
  • I have always been under the impression that, in 5e, there is actually no concept of "caster level". I thought that the only use for it was multiclassing. And the multiclassing rule doesn't actually defines something called 'caster level'. Am I wrong in saying this? – 3C273 Jul 28 '19 at 18:07
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    @3C273: You're right, which is why "spellcaster level" is in quotes in the header. It's basically shorthand for the number of equivalent levels in spellcasting classes with regular spell slot advancement. – V2Blast Jul 28 '19 at 20:22
  • @3C273 There's no formal ontology for the terms "caster level", "spellcaster level", etc., at least as far as I am aware. However, because the multiclassing rules give us a way to calculate a specific number gained from levels in various spellcasting classes, it can be easier to think of that number as being a "spellcaster level", even if the only mechanical consequence (again; that I am aware of) is to be plugged into the Multiclassed Spellcaster table in the Multiclassing rules. – Xirema Jul 28 '19 at 21:40
  • @Xirema, yeah, I see what you mean and I usually also refer to it as Caster Level. I think it would make for a better answer to make the distinction more explicit. But otherwise the answer is pretty good. – 3C273 Jul 28 '19 at 23:08
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It refers to the speed at which classes gain spell slots and new levels of spells during their progression. Full casters (like a Wizard) gain spell slots fastest, while 1/3rd casters only gain slots and new spell levels at about a third that rate.

The name "1/2 caster" and "1/3 caster" comes from the Multiclassing rules, which state that if you have levels in multiple classes capable of casting spells, you use a specific table to determine your spell slots. You only get to add half and a third of the levels in those classes (rounded down) to determine your total spell slots.

You can read more about this in the PHB on page 164, under the header "Spellcasting".

Note that these terms only refer to classes that have the Spellcasting class feature. Classes that cast spells through a different system (like a Warlock or 4 Elements Monk) don't have a caster progression and don't stack with levels in other classes when multiclassing.

For a list of classes:

Full casters

  • Bard
  • Cleric
  • Druid
  • Sorceror
  • Wizard

Half casters

  • Paladin
  • Ranger

Third casters

  • Eldritch Knight Fighters
  • Arcane Trickster Rogues
Erik
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    It’s Unearthed Arcana content, but the artificers from Wayfinder’s Guide to Eberron have an unusual progression that’s better than half-casting but not (nearly) as good as full-casting. Their multiclass rules are also unique, since they add half their level rounded up instead of rounded down. I have seen them referred to as “two-thirds” casters. – KRyan Jul 25 '19 at 17:05
  • @KRyan, the artificers appear to be rounding up rather than rounding down when the formula is applied. Some have suggested that it was an error that will be corrected. – krb Jul 25 '19 at 17:44
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    How did I know, before scrolling down, that "warlock" was not going to fit? In all seriousness, though, where (if at all) do you place something like a 4 Elements Monk? – nitsua60 Jul 25 '19 at 21:40
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    @krb: It's not an error - it was intentionally changed between the February and May 2019 UAs. You can see the change mentioned here. I believe Crawford mentioned in a Dragon+ stream or somewhere that this was in order to fix the artificer "losing" spell slots from multiclassing as a 1st-level artificer (since they're the only "half-caster" who gets spellcasting at 1st level, they uniquely experienced this issue). – V2Blast Jul 26 '19 at 06:17
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    @nitsua60 4 Elements Monk is an "it's a trap!" caster. – mattdm Jul 26 '19 at 07:58
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The fractions here come from the multiclassing rules: when figuring out what level of “multiclassed spellcaster” you are, in order to figure out your spell slots, you need to add your full level in some classes (like wizard), half your level in other classes (like paladin), and a third of your level in yet other classes (like arcane trickster). These fractions roughly correspond to how much spellcasting those classes actually give: wizards and other “1” classes get 9th-level spells, paladins and other “½” classes get 5th-level spells, and arcane tricksters and other “⅓” classes get 4th-level spells.

KRyan
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