In Generation I,
the formula for Critical Hits actually depended on a Pokemon's Base Speed Stat. The formula was
BaseSpeed / 512
and if you used a move with a high critical hit ratio like Slash, the chance was multiplied by 8:
BaseSpeed / 64
In Generations II-V,
the formula for Critical Hits was based on a fixed rate for all Pokemon called Stages. Modifiers such as Dire Hit increase the stage that Pokemon is on by a certain number of stages.
Stage 0 - 6.25% chance
Stage 1 - 12.5% chance
Stage 2 - 25% chance
Stage 3 - 33.3% chance
Stage 4+ - 50% chance
Go here for more information.
Stage (stae - guh)
- A chance of a critical hit happening. All Pokemon start off at
stage 0, or 6.25%.
In Generation VI,
the formula is exactly the same, but the stages have changed.
Stage 0 - 6.25% chance
Stage 1 - 12.5% chance
Stage 2 - 50% chance
Stage 3+ - 100% chance
