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. Each bodypart and each type of critter has its own set of possible critical hit effects. For example, living creatures with eyes tend to be particularly vulnerable to eye criticals, but other types of enemy are often more vulnerable elsewhere. 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. 

The Basic Critical Damage Calculation Formula
Nearly all critical hits do extra damage. This happens through the addition of an extra Damage Modifier, which is added over and above any damage modifier that the weapon's ammunition might already have. For example, a critical hit from a Needler pistol loaded with HN AP Needler cartridge will have, firstly, a 2/1 modifier courtesy of the ammunition, plus another damage multiplier (most typically 3/2, 2/1, or 3/1) determined by the critical effect roll.

The same way as with non-critical hits, the damage output (base damage * (possible ammo damage modifier) * critical damage modifier) is calculated first and the damage reduction effected by the target's armor is calculated second. And as with non-critical hits, the target's (natural or worn) Damage Resistance (DR) is affected by the ammunition's possible Damage Resistance Modifier.

Example
Mike is intercepted by leather-armored raiders on his way from Vault City to New Reno. He is armed with a Desert Eagle loaded with .44 magnum JHP. The weapon's base damage is 10-16. He shoots the nearest raider in the eyes and scores a critical hit, rolling 12 base damage and 18 on the critical effect table: 2x damage and roll Luck with +4 or get blinded. The ammunition has a damage modifier of 2/1 and the critical damage multiplier is 2, so the damage output before armor effects is 12 * 2 * 2 = 48.

Leather armor has a Damage Threshold (DT) of 2 and a damage resistance (DR) of 25%. The damage of 48 first undergoes a reduction of 2, leaving 46. Then the DR steps in. It is increased from 25% to 45% due to the ammunition's DR modifier of 20. The damage of 46 thus undergoes a reduction of 46 * (25% + 20%) = 20.7 (round down) = 20. The raider's base Luck is 5. The 4-point Luck bonus gives him a 90% chance of passing his Luck roll, which he does and thus keeps his eyesight. The raider takes 46-20 = 26 Hit Points of damage but keeps coming forward.

The Armor-Piercing Effect
Though the combat message accompanying these critical hits reports the armor being "bypassed", these criticals rarely bypass the target's armor in its entirety. An armor-piercing critical hit features the Weapon Penetrate effect combined with a DR modifier of 1/5, thus dividing both DT and DR by 5 and (where applicable) rounding the result down. Weapons that already have the Weapon Penetrate perk do not gain an additional DT-reducing effect.

If the weapon's ammunition has a DR modifier, positive or negative, it is factored in after the armor-piercing critical effect. This means that if the ammunition has a sufficiently negative DR modifier, an armor-piercing critical will negate 100% of the target's DR. Conversely, if the ammunition's DR modifier is poor (a big positive number), then DR will reduce a considerable percentage of even an "armor-piercing" critical hit's damage.

The positive DR modifier caused by the perk Finesse is nullified by the armor-piercing critical effect.

Example
Mike is intercepted by a squad of Enclave patrolmen on his way from San Francisco to Navarro. He is armed with an Assault rifle loaded with 5mm JHP. The weapon's base damage is 8-16. Mike decides to take an aimed shot at the head of the peskiest patrolman because the distance is too long to burst effectively. He hits his target, rolling 13 base damage and 76 on the critical effect table: 2.5x damage, armor pierced, knockdown, roll EN with -3 or get knocked out. 5mm JHP has a Damage Modifier of 2/1 and the critical damage modifier is 2.5, so damage output before armor effects is 13 * 2 * 2.5 = 65.

The Advanced power armor worn by the enemy has DT 15 and DR 55%. The armor-piercing effect of the critical hit first divides these by 5, leaving 3 and 11%, respectively. The damage of 65 undergoes a reduction of 3, leaving 62. Then DR steps in. 5mm JHP has a DR modifier of 35, increasing the diminished DR back up to 11% + 35% = 46%. Thus the remaining 62 points of damage undergo a reduction of 62 * (11% + 35%) = 28.52 (round down) = 28. The Enclave patrolman takes 62-28 = 34 HP of damage and is knocked off his feet. With his base Endurance of 8 and the penalty of -3, he has a 50% chance of staying conscious. He fails this roll and blacks out for 3 turns. When he wakes up, Mike has killed his colleagues and stolen his weapon.

Critical Burst Attacks
A burst attack is critical if its first round hits the intended target AND the attack passes its critical chance roll. Burst weapons often miss many more rounds than a 95% chance to hit would warrant, even at point-blank range. Rounds that hit the wrong target (or miss entirely) never cause critical hits.

When a burst attack is critical and rolls a critical effect, that same critical effect (and damage multiplier) is applied to every round that hits the intended target. However, each round makes an individual roll for hit/miss and base damage.

Example
On his way back to San Fran from Navarro, Vertibird plans in his pocket, Mike is intercepted by a pack of Deathclaws. The nearest animal, a Sm tough deathclaw, charges Mike forthwith and claws him for 10 HP before he can react. Mike is now armed with an H&K G11E and decides that the point-blank range warrants a burst attack. The weapon's base damage is 13-23. By a lucky break, he scores a critical hit and rolls 95 on the critical effect table. On a deathclaw, the effect is 2.5x damage, armor pierced, knockdown. The 4.7mm ammo used by the weapon has a damage multiplier of 3/2 and a DR modifier of -10. The deathclaw's thick skin endows it with 4 DT and 40% DR.

The first bullet of the 7-round burst rolls 15 base damage. This is multiplied by 3/2, yielding 22.5, which is not yet rounded at this intermediate stage but multiplied by the critical damage modifier of 2.5, yielding 56.25. This is rounded down to 56. The armor-piercing critical effect divides the deathclaw's DT of 4 by 5, yielding 0.8 (round down) = 0. Its DR of 40% is likewise divided by 5, yielding 8%, which is then further reduced by the ammunition's DR modifier: 8% - 10% = <0%. Thus, this is a case where the armor-piercing critical effect and the ammunition's favorable DR modifier combine to negate the target's armor completely -- all 56 points of damage go through.

Bullet 2: 17 * 3/2 * 2.5 = 63.75 = 63

Bullet 3: 13 * 3/2 * 2.5 = 48.75 = 48

Bullet 4: 14 * 3/2 * 2.5 = 52.5 = 52

Bullet 5: miss

Bullet 6: 21 * 3/2 * 2.5 = 78.75 = 78

Bullet 7: 18 * 3/2 * 2.5 = 67.5 = 67

The deathclaw takes 56 + 63 + 48 + 52 + 78 + 67 = 364 HP of damage and is torn to gory shreds. Mike continues towards San Fran on his quest.

Fallout 3 and Fallout: New Vegas
In Fallout 3 and Fallout: New Vegas, 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 (+5% in New Vegas) 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 hit. 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 (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 is 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.

Fallout 4
Fallout 4's critical hit system removes the chance-based critical hit trigger, replacing it with a critical meter which builds up with each successful V.A.T.S. hit and, when filled, can then be triggered by the player just before any V.A.T.S. attack, guaranteeing a hit with extra damage. The rate that the critical meter fills increases with the character's Luck.

Outside of V.A.T.S. critical hits can still randomly happen - this can be confirmed by looking at the Combat - Critical Strikes statistic in the Pip-Boy, which will be substantially higher than V.A.T.S. usage. Critical strikes outside of V.A.T.S. do not show any specific message, which can make them difficult to spot. Some chems such as Overdrive can increase critical hit chance by 25%.

Critical Damage
Weapons have a predefined critical damage which is added when a critical hit is executed, usually equal to the base weapon damage (including weapon mods). In Fallout 4 there are several ways to alter the critical hit damage. One way is through modifying a gun by adding, e.g., a Calibrated receiver or Photon exciter. These two mods add 2.0 to the critical hit multiplier. For some weapons there are receiver mods that will increase the critical damage even further, such as the Photon agitator which will add 4.0 to the critical hit multiplier.

Critical damage can also be increased in small increments by reading perk magazines and collecting bobbleheads.

DamageBase: Weapon damage, including workshop mods, but excluding perks and other bonuses.

DamagePaper: Damage displayed in PipBoy (PipBoy cuts off decimal places)

CriticalMultiplier = 1 + WeaponModBonus(2.0…4.0) + BobbleheadBonus(0.25) + MagazineBonus(0.05…0.5) + Better Criticals(0.5…1.5)

Ranged Combat
 * $${\it Damage}_{\rm Critical} = {\it Damage}_{\rm Paper} + {\it Damage}_{\rm Base} \times {\it CriticalMultiplier}$$

Melee/Unarmed Combat
 * $${\it Damage}_{\rm Critical} = {\it Damage}_{\rm Paper} \times 1.5 + {\it Damage}_{\rm Base} \times {\it CriticalMultiplier}$$


 * Missing in calculation: Weapon Prefix "Lucky" ("Critical hits do double damage")
 * Note: Tesla Science Magazine may be broken on PC, collecting these did not increase my critical damage at all.
 * Note: Mirelurks (excluding mirelurk queen) do not seem to be affected by critical damage. (only tested on survival.) (Did you hit the shell? I think I've seen crits when people have done head shots but I could be wrong)

Gallery
Критический удар Kritischer Treffer Critical Hit