Combat rating system

Combat rating system is a mechanic introduced in patch 2.0.1 which are for secondary stats on items that were previously percentage-based. Rating is converted linearly to percentage; the number of rating points needed to gain one percentage point increases with level and varies depending on the stat, but is the same for all classes. Combat ratings were introduced because percentage-based itemization would have scaled excessively when The Burning Crusade was released and the level cap rose to 70.

Secondary ratings
The following secondary ratings are currently in use:

Unlike fixed percentages such as 2% critical strike chance, combat ratings diminish in potency as characters increase in level. 2% critical strike chance is the same at every level, while 14 critical strike rating grants 5.16% crit at level 10, 2.62% crit at level 30, and 0.4% crit at level 60. 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. Combat ratings further diminish as a player gains excessive stats from rating, reducing the rating's potency even at the same player level.

All classes convert ratings into attributes at the same ratio, with the exception of Mastery, where the ratio is determined by class specialization. Below are the conversions for combat ratings at various levels:

Combat Ratings
The following table shows the amount of rating necessary for 1% of a secondary stat before diminishing returns. Due to the nature of this change, the exact rating values for diminished stats will not be listed.

Tertiary Ratings
Added in Patch 6.0.2, these bonus stats have a chance to appear on gear from certain sources. Some items and player abilities (e.g. Soul Rending) grant these stats as well.

Defensive ratings
These ratings were commonly referred to as avoidance ratings (prior to the introduction of the Avoidance stat), and are not currently itemized on end-game gear and can usually only be found on some leveling or older raiding gear, or from bonuses like Azerite Traits. For some classes and specs, these are gained passively through other stats (while protection warriors gain parry chance from strength, they also receive parry rating from critical strike rating via Riposte).
 * Dodge and parry ratings also feature diminishing returns, though the way they diminish is different from combat ratings.
 * Classes who cannot parry attacks gain no effect from parry rating.

Diminishing returns
Beginning with patch 9.0.1, combat stat ratings start to have diminishing returns above 30% stat gained from rating. This effect causes a ramping "penalty" on further stat rating gains, requiring more rating to receive an additional 1%. The amount diminished is based upon fixed stat brackets (or soft caps).

This penalty does not count secondary stat gains from fixed stat percentage buffs (such as Heroism).
 * The penalty only applies to rating gained above its minimum bracket.
 * All secondary stats have a maximum value (or hard cap) of 126%, meaning that additional stat rating has no effect.
 * This system does not apply to dodge or parry ratings, which have their own diminishing return formula.

Removed secondary stats
The following combat ratings are either no longer itemized on gear or have been removed from game. This chart is purely for historical purposes, and will not be updated to reflect future events (such as a stat squish). Notes:

Burning Crusade: Classic
The following tables display the secondary stat ratings present in  Burning Crusade Classic and the necessary amounts of rating needed per 1% secondary stat (or 1 point for Expertise, 1 skill point for Defense).

Secondary stats that are not itemized as ratings (Armor Penetration, MP5, etc.) are not included as these stats do not use the combat rating system and have the same effect at all levels.


 * There are no diminishing returns for avoidance stats in BC Classic.