Critical hit (Borderlands 2)

Calculation
Critical hits multiply the weapon's damage by two factors: first, the critical multiplier of the weapon type; second, the sum of all bonuses to critical hit damage (usually from abilities, but also from sniper rifles and a few weapon parts).
 * CriticalDamage = CardDamage × CriticalMultiplier × (100% + BonusA + BonusB + BonusC + ···)

Example: If Zer0 has five ranks in Headsh0t (+20% Critical Hit Damage) and is using a Jakobs sniper rifle (+160% Critical Hit Damage) that is listed as dealing 150 damage, then a critical hit will deal 150 × 2 × (280%) = 840 damage before being modified by elemental effects.

Weapons with the effect "Deals Bonus Elemental Damage" apply their bonus damage after the critical hit damage is calculated. That is: bonus elemental damage is not multiplied on a critical hit.

Weapon parts that contribute to increased critical hit damage: When a weapon card says "+X% Critical Hit Damage," that value indicates the total effective multiplier. For example, a non-Jakobs pistol that says "+8% Critical Hit Damage" is actually reflecting the increase from a Hyperion barrel; the multiplier of 2.15 corresponds to a total effective increase of 7.5% (rounded to 8%); the weapon doesn't actually have a built-in critical hit damage bonus (like sniper rifles do). Similarly, if a Jakobs sniper rifle says "+180% Critical Hit Damage," that means the total bonus is +180%, not 180% on top of the base 160% that all Jakobs sniper rifles have.
 * Pistols: The Hyperion barrel increases the critical multiplier by 0.15 (totaling to 2.65 for Jakobs pistols, 2.15 for all others).
 * Shotguns: The "Critikal Hit," "Critical," "Doc's," "Royal," and "Juicy" prefixes all correspond to an accessory that grants +50% critical hit damage.
 * Sniper rifles: The "Night," "Venture," "Tumtum," "Gentleman's," and "Razrez" prefixes all correspond to an accessory that grants +20% critical hit damage (totaling to +180% for Jakobs sniper rifles, +120% for all others).