Type Chart

Generation I has 15 types. Dark, Steel and Fairy do not exist yet.

The full 15×15 matrix lives on the Effective Against chart, drawn from the same records every type page reads - so the chart and the rest of the guide cannot drift apart. Read it by row: the row is the attacking type, the column is the defending type, and each cell is the multiplier, with 1.0 meaning normal damage.

Dual types multiply. Water against a Rock/Ground Pokemon such as Geodude or Rhyhorn is ×2 twice over - ×4. The chart lists single types only; you do that multiplication yourself.

Generation I quirks you must not forget

• Ghost does nothing to Psychic. This is a bug - it was meant to be super effective, and the games even tell you Psychic-types fear Ghosts. In practice it barely matters, because Lick is the only damaging Ghost move in the generation.
• Bug beats Poison AND Poison beats Bug. Both were changed to ×½ in later generations.
• Ice is neutral against Fire in Gen 1; it became ×½ in Generation II.
• Psychic is broken. Only Psychic resists Psychic, Ghost cannot touch it, and the Bug moves that would punish it are weak. Kadabra and Alakazam solo whole Elite Four rounds.
• Dragon is inert offensively: the only Dragon move in Gen 1 is Dragon Rage, which deals a flat 40 damage regardless of type.