Skyrim Wiki

The Damage statistic listed on individual weapon pages is the base amount of damage inflicted by the weapon. This amount is then modified depending on the player's skills and perks and the extent to which the weapon has been improved by smithing. The calculation is done according to the following formula (as calculated by the play testers on UESP wiki):

displayed damage =   (base damage + smithing increase) * (1 + (skill/200)) * (1 + perk effects) * (1 + item effects)
Perk Effects =   0.2 * Barbarian/Armsman/Overdraw rank level
Damage =   (Right Hand displayed Damage + Left Hand displayed Damage) * (1 + Power Attack Bonus) * (1 + Power Attack Perk) * (1 + Dual Power Attack perk) * Dual Power Attack Mod
Power Attack Bonus =   1 if power attacking
Power Attack Perk =   0.25 if power attacking and you have Savage Strike or Devastating Blow
Dual Power Attack Perk =   0.5 if power attacking with two weapons and you have Dual Savagery
Dual Power Attack Mod =   1.5 for right hand, 3 for left hand