How does a damage dealing Wizard use higher level spell slots optimally?

Question

In D&D 5e, one of the neat features for spell casting is the ability to cast spells at higher levels than the spell is originally set at. For Clerics, this makes it handy such that Cure Wounds, can be cast at a low level to cure light wounds and at a higher level to cure serious wounds. However, things become a bit more complicated for a Wizard.

If I can cast spells at higher spell levels, then does this mean that I should always pick utility spells for higher level spell slots when I'm allowed to add spells to my spellbook, and if not then when is it useful to cast a spell at a higher level slot rather than just use an existing spell of that level?

Answer 1

For this study I'm going to look at 10 spells that can be cast at higher levels.

Picking 10 somewhat randomly (ok, not really randomly, this is basically all the Evocation spells) here's the list

• L1 Magic Missile (up to 3 missiles, 1d4+1 no save/attack, higher levels more missiles)

• L1 Burning Hands (15' cone, 3d6 Dex save for half, +1d6 per spell level)

• L1 Thunderwave (15' cube, 2d8 and push Dex save for half w/ no push, +1d8 per spell level)

• L3 Fireball (20' sphere, 8d6 Dex save for half, +1d6 per spell level)

• L3 Lightning Bolt (100' line, 8d6 Dex save for half, +1d6 per spell level)

• L4 Ice Storm (20'x40' cylinder, 2d8+4d6 Dex save for half, +1d8 per spell level)

• L5 Cone of Cold (60' cone, 8d8 Con save for half, +1d8 per spell level)

• L6 Chain lightning (up to 4 targets, 10d8 Dex save for half, extra target per spell level)

• L7 Delayed Blast Fireball (20' radius, 12d6 (plus 1d6 for each round it's active but not exploded) Dex save for half, +1d6 base damage per spell level)

• L9 Meteor Storm (Up to 4 40' spheres, 20d6 + 20d6 plus Dex save for half)

Something we see quite clearly as we move up through the levels is that spells target larger areas at higher levels (from 15' cones and cubes at L1 to 20' radius, 60' cone etc.). However, for the purposes of this particular exercise, we're going to focus on upgrading all of these spells to L9 and seeing what happens. You only get 1 L9 spell slot a day, and you'd like to make sure you spend that on the best possible spell. If you want to do damage, we want to know what spell we should use in that slot.

In order to properly evaluate, let's assume there are sufficient targets that spells like Magic Missile and Chain Lightning get the full effects of the Evocation property to add your Int bonus to the spell for every target. So lets look at the damage for each spell when it's upgraded to L9:

• Magic Missile: 11*8.5 = 93.5 (8.5 per target), (43.5 single target)
• Burning Hands: (43.5 * .75)*6 = 195.75 (32.63 per target)
• Thunder Wave: (50 * .75)*9 = 337.5 (37.5 per target)
• Fireball: (54 * .75) * 11 = 445.5 (40.5 per target)
• Lightning Bolt: (54 * .75) * 11 = 445.5 (40.5 per target)
• Ice storm: (41.5 * .75) * 11 = 342.38 (31.5 per target)
• Cone of Cold: (59 * .75) * 11 = 486.75 (44.25 per target)
• Chain Lightning: (50 * .75) * 7 = 262.5 (37.5 per target)
• Delayed Blast Fireball(min): (55 * .75) * 11 = 453.75 (41.25 per target)
• Delayed Blast Fireball(max) :(89 * .75) * 11 = 734.25 (66.75 per target)
• Meteor Storm: (75 * .75) * 11 = 618.75 (56.25 per target)

Assumptions

• For spells that may affect more than 11 targets, I'm going to cap this at 11, that's the max number of targets for Magic Missile, and that should be sufficient to demonstrate the efficacy.

• That the save chance is always .5. This seems overly optimistic to me, but if we consider that Dex (or Con) and Int may cancel, then unless the opposing creature has proficiency, it's a straight up or down save. Rather than use .55 as the save chance, I use .5 to make the math easier (a save for half damage spell does .75 of it's damage every time it's used). The only real effect here is that it makes Magic Missile look a little less good.

Ok, so we need to know a few things, the first, is if we have a bunch of enemies, what tool should come out of our bag. For that, it's Cone of Cold, but Fireball is solid as well, both should be on the must take list. If we're attacking a single target, Magic Missile is a solid option, but Meteor Swarm and Cone of Cold do out pace it.

Overall, what we can tell here is that the early level spells compete well as they are upgraded with the later level spells. They are marginally weaker and affect fewer targets, but they do actually scale rather well to where it's not a waste of a spell slot to cast them at higher levels.

As to whether I'd skip high level damage spells in favor of utility spells, I don't think so. Battle fields should get bigger as you level up and it will be important to have the wide area spells in your bag at those levels. The ones to skip might be things like Chain Lightning as the evocation casting feature "Sculpt Spell" means that you don't have to worry about having your party members in the areas of your spells.

Another factor to consider is spell slots and spell acquisition. While you can find or maybe even purchase high level spells and copy them to your spell book, this does have a cost and is wholly dependent on your DM. You are only guaranteed 44 or so spells in your career so you want to make those selections count (right now this is enough to take all but about 14 of the published spells, which is plenty). The other factor is preparation spots and utility. This analysis shows that spells like Thunderwave and Fireball are quite similar, it might be a good idea to take the lower level one as it can be cast in more slots.

Answer 2

You have to make a spell by spell comparison every time you level up

And comparing spells is more art than science.

Multi-target damage

Let's assume you have 2 enemies, 10 HP each. You do 6 damage to both of them, they still can hit you on their rounds. If you do 10 damage to one of them, you will be hit only once. For optimization, 2 x 6 < 10. There is no easy way to measure efficiency for multi-target attacks, but on other boards the following calculation is accepted:

• 100% for the first target
• 50% for the second (1/2)
• 33% for the third (1/3)
• and so on

So a spell that does 12 damage for 4 target is roughly equivalent to a spell that does 12 + 6 + 4 + 3 = 25 to a single target, not 48. And enemies usually do not do you the favor of piling up like this, definitely not 11 of them like wax eagle suggests in his answer.

Damage of the slot

Fireball does 8d6 damage for a 3rd level slot, Burning Hand does 5d6. It also has worse reach and smaller area. Fireball wins hands down.

Cone of Cold does 8d8 (average 36), Fireball 10d6 (35) for a 5th level slot. Fireball only does slightly less damage, and still has a better shape. Unless I know I am up against fire resistent creatures, I would still take that one. However for a 9th level slot, Cone of Cold does 12d8 (54) while Fireball does 14d6 (49) damage.

If two spells have similar shape and damage in the same slot, pick the one with the lower base level. If you can take them out with a Fireball in the 3rd level slot, why waste a 5th level slot, you have fewer of those.

Spell progression is not parallel, if one spell was better in a 2nd level slot, it might not be better at a 5th. Take Burning Hands vs Thunderwave; 1st level slot does 10.5 vs 9 damage, 5th level slot does 24.5 vs 27.
For this reason comparing spells only in 9th level slots is useful if you actually have those, and no other slots. (meaning never)

Damage types

A Fireball is useless even in a 9th level slot against someone who is immune to fire.

• Poison is the least useful (verging on useless), most undead, devils and demons are immune, and many other creatures have resistance.
• Necrotic is much better, but still a clear second. Mostly undeads are immune or resistant.
• Fire and Cold are roughly equivalent, more creatures resist fire, but also more are vulnerable to it. Most incorporeal undead are immune to cold.
• Lightning, Radiant, Acid, Psychic, Thunder and Force are very rarely resisted.
• Bludgeoning, Piercing and Slashing damage from spells are only resisted by swarms.

Save or Attack

Both have their pros and cons, but if every other parameter is equal, an Attack roll is far superior in most cases. Many monsters have Magic Resistance and even Legendary Saves, but only the Tarrasque is protected against (ranged) attack rolls. Also it is much easier to gain Advantage on attacks than to force disadvantage on a save.

Attacks

You have Disadvantage on ranged attack rolls, if you are adjacent to an enemy.
Most spells with attack rolls target single creatures, or you have to split the damage, like Scorching Ray.

Saves

The type of save matters a lot, a Stone Giant has a better chance to succeed on a Con save even with disadvantage, than on an simple Cha save against DC 15. So prepare diverse spells, quite often the description provided by the DM tells you what they are most sensitive to:

• Strength saves against caster and skirmisher types
• Dexterity saves against big burly warriors and casters
• Constitution saves against caster and skirmisher types
• Intelligence saves against big burly warriors
• Wisdom saves against big burly warriors and skirmishers
• Charisma saves against the ugly ones

Save for half
As wax eagle points out a spell that allowes a save for half is only worth about 75% of a spell that does not.

Save for nothing
These spells can be considered 25% weaker than spells that do half damage even on a save.

Other effects

Some spells have secondary effects besides direct damage, like the push of Thunderwave. It is hard to put a number on them, but still you have to consider how useful it is for you.

Conclusion

Every time you level up and gain a higher slot, you have to calculate the damage of the spells that just became available for you and compare it to your current spells. If the difference is big, take the new one as one of your free spells.
You have to take into account the campaign setting as well. If the DM only throws kobolds at you, even on 10th level, Fireball is enough. Cone of Cold will not make them any more dead, but it will eat up your 5th level slot.

You have to make this mental arithmetic every time you prepare spells as well.