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Weapons spread determines the accuracy of a ranged weapon in degrees. Formulas here were taken from the GECK wiki for Fallout 3.

Spread computation

The total spread is the largest of the aim spread value due to the character aiming and the weapon spread value due to the weapon itself. Therefore, no matter how skilled you are with the weapon or what perks you have, your weapon will always have a slight amount of spread. The exceptions being weapons with 0 spread.

Aim Spread

State Effects

State effects combine multiplicatively.

  • Crouching reduces spread by 40%. (multiplier: 0.6)
  • Using Aim down sights reduces spread by 65%. (multiplier: 0.35)
  • Accordingly, doing both reduces spread by 79%. (multiplier: 0.21)

Mobility Effects

Mobility effects are additive, but under the game's default settings, they always sum to 1, and hence simplify out to being ignored; if the appropriate game settings are tweaked, they can be used to apply different penalties across walking, running and remaining still.

Skill/Weapon Condition Effects

These combine additively, but by default, Weapon Condition is always 0, so only the Skill Effect matters; if the appropriate game settings are tweaked, weapon condition (from 0 to 100%) times a constant will combine additively with skill.

The appropriate skill (Guns, Energy Weapons or Explosives) reduces spread by 0.5% (from 50% up to 100%) per skill point. (multiplier: from 0.5 to 0)

Limb Condition Effect

Damage to limbs increases (pre-perk) spread.

  • ArmPenalty is 0 with no crippled arms, 0.5 when the right arm is crippled with a one-handed weapon, 0.25 with one arm crippled with two-handed weapon, 0.5 when both arms are crippled with two-handed weapons.

Weapon spread

Weapon spread is equal to the Min Spread stat of the weapon in degrees. The weapon condition has no effect on the weapon spread.


Fallout: New Vegas Prior to patch, ammunition that had a spread modification effect (like the 12 gauge shotgun shell) applied it to the aim spread instead of the weapon spread.

External links