Roll a d12

The argument

Greataxe or greatsword, settled

Same cost, same weight, same damage type, and one of them is better. The gap is half a point before fighting styles and a full point after one, in the direction most tables guess wrong.

Great Weapon Fighting lets you reroll a 1 or a 2 once and keep the new result. A greatsword has two dice that can each catch that reroll and a greataxe has one, so the style that sounds like it should rescue the big single die actually pulls the two further apart.

The greataxe still wins one thing, and it is not average damage. On a critical hit you roll the damage dice twice, so both weapons top out at 24. The greataxe gets there about nine times more often: 2d12 rolls a maximum once in 144 attempts, 4d6 once in 1,296. If you want the roll that occasionally deletes a monster rather than the roll that reliably hurts it, take the axe.

Totals

Range and average, one die to eight

A single d12 averages 6.5, the highest of any single die except the d20. One d12 on its own is the swingiest damage roll in the game, and that is the whole appeal.

In play

What actually calls for a d12

Not much, and that is the d12's whole reputation. One hit die, two weapons, and a crit rider.

Barbarian hit die

1d12

Greataxe damage

1d12

Lance damage

1d12

Half-orc savage attacks, extra die on a crit

1d12

Levelling a barbarian and deciding whether to roll for hit points? The d8 page works through roll against fixed value for every hit die in the game.

Questions

Is a greataxe or a greatsword better?

The greatsword, on both counts. A greataxe is 1d12 and averages 6.5; a greatsword is 2d6 and averages 7. Two dice also cluster around the middle instead of spreading flat, so the greatsword is steadier as well as slightly higher. What the greataxe buys you is variance: it maxes out roughly nine times more often, which is a real argument if you want swing rather than reliability.

Does Great Weapon Fighting change the answer?

It widens the gap rather than closing it. Rerolling 1s and 2s takes the greataxe to 7.33 and the greatsword to 8.33, because the greatsword has two dice that can each benefit from the reroll and the greataxe has one. The style that sounds like it should rescue the big single die does the opposite.

Which classes use a d12 hit die?

Barbarians, and nobody else. It is the largest hit die in fifth edition, and combined with rage damage resistance it is most of why a barbarian is so hard to put down.

What is the average roll on a d12?

6.5. For several dice, multiply: 2d12 averages 13, 4d12 averages 26, 8d12 averages 52. The table above lists the range and the average for every count from one die to eight.

What is a d12 actually for?

Barbarian hit points, greataxe and lance damage, and the extra crit die a half-orc gets from savage attacks. It is the least used die in the set by a comfortable margin, which is why most tables have one that still looks new.

Is a d12 a dodecahedron?

Yes, twelve regular pentagonal faces. It rolls further than any other die in the set except the d20, because it is the closest of the two to being a sphere.