Critical Hit

Critical Hits are hits which cause extra damage, or other side effects. If a hit is successful, it may become a critical hit if it passes Critical Chance. The effect of the hit is determined by another roll, on the critical hit table. Effect depends on the area hit, and various unknown variables. The effect of a critical hit can be modified by the Perk Better Criticals.

Note that the chance for a critical hit is determined by Critical Chance, and is not the same as critical effect. See Aimed Shot in the Combat section for more info.

Critical effects
This is the critical hit table for human men. Tables for other critters are different, and can be found here.

Example
The following example is a bit tricky: you might want to open another window with reference material.

Situation: Alvin York (S5, P9, E5, C3, I5, A10, L10) is carrying a Hunting Rifle and has a Small Guns skill of 150%, and one of his traits is Finesse. He spies an armored gentleman, wearing Metal Armor some distance (8 hexes) away, and decides to make an aimed shot for the eyes. This is what happens:

Alvin's base to hit is (150 - 30) + (8 * 9) + (No penalty) - (15 + 5) + 4 - 60 = 112%, a definite hit! Alvin's critical chance is (1 * 10) + (10) + (a mysterious number) = Critical hit! Alvin rolls 1d100 for the critical effect table, and gets 85. His damage is (20 * 3) - (armor ignored) = 60

Mr. Metal Man loses 60 of his 70 hp, and staggers around blindly. With his remaining 4 of 10 action points, Alvin advances closer to Mr. Metal Man, who lost his responding turn as a result of the critical.

Alvin fires at the eyes again. BTH is the same, and CC is successful. CE rolls a 95.

Mr Man screams in agony, as a round of ammunition pierces his visor, blinding him. He falls slowly to his knees, bewildered and overcome. Bleeding from his helmet, he keels over, killed by the 56 damage AND the "instant kill" effect. With his remaining 4 action points, Alvin York marries Gracie Williams, has seven children, and dies at the age of 76.

Fallout 3
In Fallout 3, the critical hit feature is simplified from Fallout and Fallout 2. When a weapon is fired, it has a predefined, specific percentage chance of getting a critical hit (with a few exceptions, see below), which is essentially just added damage to the original base damage (the damage that will be dealt if the PC does not score a critical hit). This obviously sounds much simpler than the system of the first two games, but it is still more complex than it sounds.

Critical Chance
The player's base critical chance is determined by the Luck SPECIAL statistic and the Finesse, Survival Expert, and Ninja  perks. The maximum possible base critical chance is 18% with ranged weapons, and 33% with unarmed and melee weapons. The base critical chance is modified by a weapon's critical multiplier to obtain the final chance to score a critical hit. Also, a +15% critical chance bonus is added to all attacks in V.A.T.S.

Critical Damage
Every weapon has a predefined critical damage, which is the damage added during a critical. The only modifier to critical damage is the Better Criticals perk, which gives criticals a 50% damage bonus. This is a lot more impressive than it sounds. For example, the Wazer Wifle has a critical damage of 28, but with the perk, the critical damage becomes 42, making 70 damage on a non-sneak critical and 140 damage on a Sneak Attack Critical.

Sneak Attack Critical
A Sneak Attack Critical occurs when successfully attacking an opponent while being [HIDDEN] by using one's Sneak skill. Successfully hitting the target will result in a guaranteed critical strike. This more specialized critical strike doubles the damage generally done with a non-sneak attack critical. For example, Lincoln's Repeater has a base damage of 50 (yours might be different with perks, weapon condition, and skill) and a critical damage of 50, so a basic critical hit would do 100 damage (unless you have the Better Criticals perk). When a sneak attack critical dealt, the damage completely doubles, so the Sneak Attack Critical gives a whopping 200 damage (250 with Better Criticals).

Fallout: Brotherhood of Steel
In Fallout: Brotherhood of Steel, the system works much like Fallout 3, when a weapon is fired, it has a predefined, specific percentage chance of getting a critical hit) which is just to exceed the maximum limit of damage for a weapon.

Критический удар