How does Empower Spell interact with criticals?

Question

How is the the total damage of a spell calculated, if it is enhanced by the Empower Spell metamagic feat and a critical hit is rolled?

According to the d20 SRD Empower Spell feat entry:

Benefit: All variable, numeric effects of an empowered spell are increased by one-half.

Still according to the SRD in the note about Multiplying:

Sometimes a rule makes you multiply a number or a die roll. As long as you’re applying a single multiplier, multiply the number normally. When two or more multipliers apply to any abstract value (such as a modifier or a die roll), however, combine them into a single multiple, with each extra multiple adding 1 less than its value to the first multiple. Thus, a double (×2) and a double (×2) applied to the same number results in a triple (×3, because 2 + 1 = 3).

So, if for example, a 5th level wizard casts an Empowered Shocking Grasp (5d6 damage) and scores a critical hit, will she:

• roll 10d6, the add 50% of the total (i.e. the Multiplying rule does not apply), or
• roll 5d6 plus 50% plus another 5d6 (i.e. by the Multiplying rule: 5d6×2×1.5 = 5d6×(2+0.5))?

Answer 1

Empower Spell adds 50% of the variable, numeric effects of a spell. The number of dice is not a variable, numeric effect (e.g., you roll 5d6 on a shocking grasp -- that number is not the variable being referred to, the result of rolling it is).

Therefore, if you normally roll 5d6 on a shocking grasp and you score a critical hit, then you will roll 10d6. Taking the result of 10d6, you then add 50% of that result to get the empowered value.

Shocking Grasp in your example grants (5*2)d6 on a Critical Hit.

Say you score 36 (a hair above average): then you will add 50%, or 18, to the result, coming to 54 damage.

The example given in the PHB is of magic missle and describes the same process -- for each 1d4+1 missile, multiple the 1d4 result by 1.5.