From Bulbapedia, the community-driven Pokémon encyclopedia.
The Bulbagarden Tier System is an alternative to the Smogon tier system, first drafted up in early 2011.
There are 7 tiers, named simply "Tier 1" up to "Tier 7". Tier 1 is for the least used Pokémon, whereas Tier 7 is for the most used.
The goal of this tier system was to promote variety instead of simply rank Pokémon by their power levels. As such, it is entirely based on usage, not having a ban list either.
Promotion and Demotion
Each Pokémon has what is called its measure of relative representation within a tier. This is a measure of how dominant a Pokémon is within a tier, or how often it is used compared to other Pokémon within that tier. It is calculated by dividing that Pokémon's actual representation within that tier (how much it is used compared to the tier as a whole) by the total actual representation of other Pokémon within that tier, as in this formula:
The system is designed so that the totals of all the relative representations of each Pokémon can be used to measure the degree of skew within that tier. If every Pokémon is being used equally within a tier, the total can be proven to be at the minimum value, which, for a tier with n Pokémon in it, is simply equal to the following:
Each Pokémon also has a fair share of relative representation, which is simply the relative representation if each Pokémon within that tier were to be used equally.
If a Pokémon is used much more than its fair share, it becomes promoted to a higher tier. If a Pokémon is used much less than its fair share, it becomes demoted to a lower tier. This is expressed in terms of a ratio to the fair share. The current cutoffs, as of February 2011, are:
| Tier Cutoffs