Damage Order of Operations

To determine how much damage an attack will do to a unit, follow these steps.

1. If the unit has shield HP, subtract shield armor upgrades from the damage.
2. Apply the damage to the shield HP.
3. If any damage remains, subtract the unit's armor from the damage.
4. If the damage is Explosive or Concussive type, modify it based on the unit's size.
   1. Explosive damage deals 100% to large units, 75% to medium units, and 50% to small units.
   2. Concussive damage deals 25% to large units, 50% to medium units, and 100% to small units.
5. Apply the remaining damage to the HP. If the attack did no damage to Protoss shields and the remaining damage is one-half or less, it will do a half-point of damage.

Spell Damage

All spells except for Yamato Cannon and Nuke ignore unit armor. Yamato Cannon does 260 explosive damage to a single target. Plague also ignores Protoss shields and does damage directly to the unit or buildings HP.

References

Damage Order of Operations