They are a resource used to cast magic, a measurement of magical stamina if you will.
Smaller spells take less energy to cast so use lower level spell slots.
Larger spells take a bit more oomph, and so need a proportionately higher level spell slot.
When a character casts a spell in D&D, a spell slot of the appropriate level is then used up to show that energy is spent.
Spellcasters can only channel so much magic before they need a rest to recuperate so they have a limited number of spell slots available to them each day.
It’s important as both a player and a dungeon master to make sure you understand how spell slots work. Spell slots are an area where a lot of people get confused so it’s especially helpful to have someone with a firm grasp of how they work at the table!
Spellcasting may seem intimidating but I promise it’s not too hard once you get used to it :)
Let me show you!
How do spell slot levels work?
As I mentioned, spell slots are how D&D track magical stamina and the energy needed to cast different power-level spells and turn it into a game mechanic.
There’s one thing that often trips people up when first learning the system …
Spell levels are NOT the same thing as character levels.
It’s a bit unfortunate that they called them “spell levels" to be honest!
Personally I find it a bit less confusing to refer to spell levels as spell “tiers” in my head.
I.e. I would refer to the spell Bane as a “1st tier enchantment spell”, rather than “1st level enchantment spell”.
You might like that, or a different word may may make more sense to you.
The more powerful a spell, the more energy it takes to cast.
Therefore, the more powerful a spell, the higher the level of spell slot it must be cast with.
9th tier spells are rarely cast by any but the most legendary figures in the world, such as Baba Yaga.
How does upcasting work?
Whilst a lower tier spell slot doesn’t have enough energy to cast a higher level spell, you can always cast a lower tier spell using a higher level slot.
Spells usually become stronger if you “upcast” them by using a more powerful spell slot than the minimum required.
Let’s take the third level spell Fireball as an example.
Fireball is a powerful spell so needs to be cast with at least a 3rd level spell slot. A first or second tier spell slot are not powerful enough.
You can also cast Fireball with spell slots higher than 3rd level. In fact, Fireball gets more powerful when a caster uses more of their magical energies when casting the spell.
In the case of the spell Fireball, the damage increases by 1d6 for each slot level above 3rd.
Therefore a Fireball cast with a 5th level spell slot does the normal 8d6 damage of the base 3rd tier spell, + 2 d6 extra damage as the spell is cast two tiers higher than its base.
Another example of upcasting ...
For the spell Hold Person, you can target a whole extra person for every extra spell slot level that is used when casting.
The difference between known spells and prepared spells?
“Known spells” is used to refer to spells you know how to do. Just knowing a spell doesn't automatically mean you can cast it though!
Knowing lots of spells that you could cast doesn’t help much when you don’t have the ingredients ready to cast them!
Some classes such as druids and clerics need to choose which spells they will be able to use each day from a list of all the spells they have knowledge of.
This is called preparing spells.
Preparing spells can look like however you want, praying to your God, book marking pages in your spell book, sorting through material components etc.
The point is just that character’s who prepare spells need to choose which from a wide variety they want to be able to use today.
They are prepared in the first hour after waking, before the adventuring day begins.
Other classes like bards or sorcerers are spontaneous casters and don’t need to prepare spells.
How many spell slots do magic users get?
The number of spell slots a character has depends on their class.
“Full casters” such as wizards or bards usually have far more spell slots than “half casters” like paladins.
Each class has their own way of determining how many spells a character can cast.
I’ll be going through classes individually in future posts so I’ll dive into the nitty gritty of class specific spell casting rules there!
When do spell slots return?
When you rest, you get some of your energy back. This is as true for spell casters as it is martial fighter.
After a long rest, all of the expended spell slots are restored and mages are ready to cast again.
Warlocks are a bit unusual in that they get their spell slots back after a short rest as well. Lucky sods!
This means Warlock’s can really shine in long adventuring days or dungeon crawls where endurance is important.
There are also some class specific ways spell slots can return. For example, sorcerers can exchange sorcery points for spell slots, wizards can use Arcane Recovery.
Again, I’ll save that for my posts covering each class individually!
For now, just know that the general rule is that everyone regains expended spell slots after a long rest, and Warlocks get them back on short rests as well.
Spell slots are usually a very precious commodity!
What spells don’t need spell slots?
There are some forms of magic that don’t require spell slots.
These are cantrips, ritual spells and traits & abilities.
Cantrips are minor magical effects, not strong enough to be counted as a full spell. You may see them referred to as “Level 0 spells”.
Cantrips can be utility based or damage dealing, and some like Produce Flame can be both.
Cantrips can be case as many times as you like in a day and often become a casters “Plan B” attack, once they are out of spell slots.
Ritual spells can be any spell level and can be cast by spending a spell slot as normal, or cast as a ritual without using up a spell slot.
It takes a while to prepare and enact the ritual so each spell takes exactly ten minutes longer than normal to cast as a ritual.
Spells also cannot be upcast if they are cast as a ritual.
Ritual spellcasting is a little niche. Not all spells are ritual spells and not all classes can ritual cast!
In order to cast a ritual spell, the spell must have the tag “ritual” and the casters class must specify that they can ritual cast.
Traits and Abilities
Some classes and races also have certain traits and abilities that allow players to cast spells without consuming spell slots.
We could be talking about a Warlocks Eldritch Invocation, the Fey Touched feat, or a Tiefling’s Infernal Legacy.
Generally a character will only have one or two abilities like this so whilst it can be a bit complicated, it doesn’t have to be overwhelming to keep track of.
How multiclassing affects spells
Ok! Multiclassing can complicate spell casting a bit more. To do it justice, I will go over this topic in a separate post as well!
In a nutshell though...
Multiclassing in spellcasting affects the number of spells known, how (and if!) spells are prepared, and the number and level of spell slots available.
i.e. it affects what spells you can cast, the way you cast them, and how much magical energy you are able to channel.
If you’re new to D&D and spell casting, I really recommend you leave multiclassing across spellcasting classes until you’ve found your feet a bit more.
You’ve got enough things to try and remember!
A cheeky recap of how spell slots work in D&D 5e
We’ve covered quite a bit today!
We’ve seen that spell slots are how D&D represents the energy needed to cast spells, and are how the game manages this resource as a mechanic.
Spell slots are sorted into different tiers from 1 to 9 based on the amount of magical energy they consume.
When casting a spell, a mage needs to use a spell slot of the same spell level or higher, in order to have enough power to cast it.
Casting a spell with a more powerful spell slot often leads to a more powerful spell effect.
And lastly, spell casters can only channel so much magical energy in a day, so they have a finite number of spell slots.
Used spell slots replenish after a long rest, and for some classes on short rests.
The Final Takeaway
Phew! It’s a lot!
Spell casting can seem really complicated and overwhelming when you first look at it.
If you’re still feeling that way after reading all the way through then that’s ok!
I didn’t understand spell slots when I began DMing, but with practice I learned soon enough. You will too :)
If you’re a dungeon master just starting out, don’t worry if you need to flick back to the rules book to check things during game - that just shows that you care about consistency and fair play!
I recommend you just concentrate on getting an understanding of the basics covered here. You can learn the specifics based on what classes you have in your party, or by looking closer at the rules as and when they come up.
There’s nothing wrong with not knowing everything immediately :) You’ll get there!
I believe in you :)