Whenever you use a skill or attack, you have a chance to deal a Critical Strike.
Critical Strikes are rolled on a per-action basis, not per-monster. So each time you use a skill, the Critical Strike roll is made once and only once. If you roll a Critical Strike, you will deal Critical damage to all enemies hit by the skill. Struck enemies cursed with Critical Weakness can cause an initial roll that comes up non-critical to potentially become a critical strike.
Critical Strikes do more damage than normal, based on your Critical Strike Damage Multiplier. All characters have a base Critical Strike multiplier of 150%, meaning a critical strike does 150% of normal damage. This multiplier can be increased with various skills and modifiers on items. This multiplier will be applied to all damage components (whether physical, elemental, or direct chaos damage) within a hit.
For instance, with a multiplier of 250%, if you deal a Critical Strike with an attack that normally does 100 physical damage and 10 cold damage, you will instead deal 250 physical damage and 25 cold damage.
The multiplier value is modified by talents multiplicatively, for instance if you have +40% and +20% modifiers, the resulting crit multiplier will be 150*(1+0.4+0.2)=240%, meaning that critical strikes deal 240% damage of normal hits.
The chance to deal a critical strike is taken from the weapon used to perform an attack or attack skill, and in the case of spells, each spell has its own critical strike chance, which is listed in the skill gem's description.
This value can be increased by increased critical strike chance modifiers from spells and gear. For example, if you are using a weapon with 5% chance to crit, and you have 50% increased critical strike chance, you will have a 7.5% chance to score a critical strike.
Critical chance can not be less than 5% nor more than 95%.
Critical Strike Chance and Critical Strike Damage Multiplier are calculated separately for each spell and weapon attack. All weapons and damage-dealing spells have a base Critical Strike chance listed on them. This only affects your chance to critical for attacks made with that weapon or spell. For instance the critical strike chance on a wand does not affect your chance to critical with a spell.
Basic Critical Strike Passives are:
- 3 x Critical Strike Chance (20%)
- 15 x Critical Strike Chance (15%)
- 13 x Critical Strike Multiplier (10%)
Notable Critical Strike Passives are:
- 1 x Assassination (40% Increased Critical Strike Chance, 20% Increased Critical Strike Multiplier)
- 2 x Bloodthirst (45% Increased Critical Strike Chance)
- 1 x Mental Acuity (30% Increased Critical Strike Chance, 20 Intelligence)
- 4 x Cruelty/Heartseeker/Throatseeker (30% Increased Critical Strike Multiplier)
For a total of 39 Critical Strike Passives granting 445% Increased Critical Strike Chance, 250% Increased Critical Strike Multiplier and 20 Intelligence.
Other Passives affecting Critical Strike include Critical Strike for Spells Passives, Dual Wielding Passives, One-Handed Melee Weapons Passives, Two-Handed Melee Weapons and Specific Weapons (Bows, Claws, Daggers, Staves, Maces, Swords and Wands) Passives.