The Barbarian uses a d12 Hit Die in the 2014 rules. This is the largest standard Hit Die used by a normal player-character class and contributes to the Barbarian's reputation for exceptional durability.

Hit points at 1st level

At 1st level, a Barbarian begins with:

12 + Constitution modifier

The die is not rolled at 1st level.

The maximum value of the d12 is used.

A higher Constitution score therefore increases the Barbarian's starting durability immediately.

Hit points at later levels

For every Barbarian level after 1st, the character gains:

1d12 + Constitution modifier

or can use the fixed average:

7 + Constitution modifier

depending on the table's normal level-up rules.

Why the d12 matters

A large Hit Die gives the Barbarian a strong hit-point foundation.

That durability combines particularly well with Rage resistance to common physical damage.

The class is therefore not durable because of only one feature.

It combines high hit points with damage mitigation and later survival features.

Spending Hit Dice during short rests

Hit Dice are also a healing resource.

During a short rest, a character can spend available Hit Dice and recover hit points according to the normal resting rules.

A Barbarian spends d12s for Barbarian Hit Dice.

Constitution also contributes to the healing gained from each spent Hit Die.

Multiclass characters

A multiclass character can have different Hit Die types.

For example, a character with Barbarian levels and levels in another class keeps track of the Hit Dice granted by each class.

The Barbarian levels still provide d12 Hit Dice.

The other class uses its own Hit Die type.

Hit Die versus Hit Dice

“Hit Die” is singular.

“Hit Dice” is plural.

The question “What is the Hit Die for a Barbarian?” refers to the type of die the class uses: a d12.

A character with several Barbarian levels possesses several d12 Hit Dice.