Combat rating system Combat rating is a mechanic introduced in patch 2 . 0 . 1 which are for combat stats on items that were previously percentage based ; rating is converted to percentage based on values that Blizzard chooses . Ratings were introduced because percentage based itemization would have scaled excessively when " " was released and the player cap rose to 70 . Combat rating types . The following combat ratings are currently in use : Deprecated or removed in Warlords of Draenor . The following combat ratings have been deprecated and are no longer in use : Deprecated or removed in Mists of Pandaria . The following combat ratings have been deprecated and are no longer in use : Deprecated or removed in Cataclysm . The following combat ratings have been deprecated and are no longer in use : Deprecated or removed in Wrath of the Lich King . The following combat ratings have been deprecated and are no longer in use : Combat skills . Unlike fixed percentages such as 2 % critical strike chance , combat ratings diminish in potency as your character increases in level . 2 % crit is the same at every level , while 28 critical strike rating grants 4 % crit at level 34 , 2 % crit at level 60 , and 1 . 27 % crit at level 70 . This allows Blizzard the ability to create and add new and better items to the world without eventually reaching a point where every character has a 100 % chance to critically strike . Below are the conversion for level 60 , level 70 , and level 80 combat skills : Prior to patch 2 . 0 . 1 , Weapon Skill reduced the percentage of damage lost due to glancing blows . Between patch 2 . 0 . 1 and patch 2 . 3 , Weapon Skill gave player + 0 . 1 % to their critical strike rating per weapon skill against monsters above their level . As of patch 2 . 3 , all items which previously had Weapon Skill Rating or Feral Combat Rating now have an equal amount of Rating . From the 2 . 3 PTR patch notes : " We have added a new stat and associated rating called expertise and expertise rating . Expertise rating converts to expertise at the same rate that weapon skill rating formerly converted at . Each point of expertise reduces the chance for your attacks to be dodged or parried by 0 . 25 % . " Patch 3 . 1 increased the effectiveness of armor penetration rating by 25 % . Unlike Weapon / Feral Combat Rating , Expertise does not have diminishing returns beyond 20 rating . For players , this means that once the hit cap has been reached , one can begin stacking Expertise to increase damage potential against mobs with high dodge / parry . Melee DPS classes won ' t benefit much from the - parry ( as they should be behind the target ) , however dodges do make up a considerable chunk of lost damage . Druid tanking items with Expertise , such as Earthwarden , will be more valuable for consistent threat generation since a parried / dodged Mangle can be devastating . Since Expertise is ' capped ' by the target ' s chance to dodge / parry , the ideal rating varies per mob . The average level 73 boss has a 6 . 5 % chance to dodge . Completely negating a 6 . 5 % chance to dodge would require 102 Expertise rating at level 70 , assuming the character had no talents which reduced his target ' s dodge chance . Defense skills . The impact on the defense skill system is slightly more complicated . This skill actually grants a percentage - based benefit already ; every 25 points of defense skill grants a 1 % dodge chance , 1 % parry chance , 1 % block chance , 1 % increased chance to be missed and 1 % decreased chance to be critically hit by physical attacks . Below are the defense rating values needed to achieve 1 % of each effect : From Patch 3 . 2 onward . All of these Ratings have the same " point cost " when determining the level of an item . ( See the article on Item values for an in - depth discussion . ) For comparison , 1 point of Block Value , which decreases the damage taken when a block occurs by 1 , costs 0 . 65 as much as 1 point of any of these Ratings . Resilience . Resilience reduces the effects of all types of critical hit s ( both physical and spell crit s from players or mobs ) . Resilience has three components ; it reduces the chance you will be critically hit by " x " % , and it reduces the damage dealt to you by crits that land by 2 " x " % and finally reduces all pet - and player - caused damage by an additional " x " % . " x " is the percentage resilience granted by a given resilience rating . In 2 . 4 an additional effect was added to resilience . It reduces the amount of mana drained or burned by mana draining effects by 2 " x " % . PvE tanks usually have high enough + defense values so that mobs won ' t crit them at all , thus in PvE this is not an important statistic . Historical Note : Prior to Patch 3 . 0 , the Survival of the Fittest feral druid talent only reduced the druid ' s chance to be crit by 3 % at most . Thus , for druid tanks , resilience could actually be more useful than defense to reach crit immunity ( with the talent , a raid boss ' s crit chance at level 70 was 2 . 6 % before Defense Rating or Resilience was applied ) . This is no longer true as of patch 3 . 0 , where druids can become completely immune to crits from mobs though SotF alone , without defense or resilience . The formulas below are still valid if you don ' t have 3 / 3 of this talent . For a level 70 druid : 60 defense rating = ( - 1 % crit , + 1 % miss , + 1 % dodge , + 1 % parry , + 1 % block ) 39 . 4 resilience rating = ( - 1 % crit , - 2 % crit damage ) 14 . 7 agi = ( + 1 % dodge , + 0 . 58 % crit , + 29 . 4 armor ) The conclusion is that if your goal is to become a crit - immune druid , you can swap 60 defense rating for 39 . 4 resilience rating + 29 . 4 agi . This is because ( 1 % miss and 1 % dodge ) = 2 % dodge , see also Attack Table for this . So this trade off gives you the same crit immunity and gives even slightly better damage mitigation because of the use of Agility . This trade - off is also good for the extra crit and armor , which are both useful for feral tanks . Looking at normal stats of defense rating and resilience on armor and weapons , it is easier to get crit immunity through resilience than through defense . This is not true for Warrior s and Paladin s as they can Block and Parry and therefore get much more benefit from defense rating than feral druids . Leveling . Each time you go up a level , the amount of rating needed to get the same benefit will increase . An example of the scaling involved would be the current implementation of Agility which has always worked this way in the live game , requiring more agility for the same critical strike chance as you go up in level . Diminishing returns . As of patch 3 . 0 . 2 , combat ratings that affect avoidance stats now have diminishing returns . Combat Ratings formula . The following formulas give the amount of rating required to achieve a 1 % bonus . They can be derived from two sources , the values stored in the client and extensive testing done by the author of the Rating Buster addon , and are completely accurate ( each method gives the same values within the margin of error for 32 - bit floating point precision , or 10 ^ - 7 ) . Values are calculated with below formulas : The 70 - to - 80 formula may change in future patches , but is current as of Patch 3 . 0 . 3 . 9183 ( verified Dec 2 , 2008 ) . 1 ) " - " is here because the variable that Blizzard calls speed is actually the period between two swings / shoots . Actual speed is increased . 2 ) Paladins , Shamans , Druids and Death Knights receive 30 % extra value for this stat ( effective base value is 13 ) 3 ) Unlike the other ratings , Haste Rating → Speed / Cast time conversion isn ' t linear ; see Haste Historical note . Prior to version 2 . 0 . 1 , item bonuses didn ' t use the Combat Ratings System . Instead , items had equip and on - use bonuses that increased the underlying value directly . For example , instead of increasing the wearer ' s Crit Rating by 14 and the wearer ' s Dodge Rating by 12 , the old pre - 2 . 0 . 1 Stormshroud Shoulders added + 1 % to the wearer ' s Crit chance and + 1 % to the wearer ' s Dodge chance . When Blizzard made the conversion to 2 . 0 . 1 , all existing items with the old + crit % , + defense , etc . values were converted to their equivalent values in the new Ratings system scaled for a level 60 character . For example , an item that previously gave + 10 Defense Skill now gives + 15 Defense Rating . ( Conversions that would have resulted in a fractional Rating were rounded down to the nearest whole number ; e . g . an item that previously gave + 3 Defense Skill now gives + 4 Defense Rating . )