Type Chart

The complete Generation I effectiveness matrix, including the bugs that make Gen 1 play unlike every later generation.

Type Chart (Generation I)

15 types - no Dark, no Steel, no Fairy

Generation I has 15 types. Dark, Steel and Fairy do not exist yet. Read the table by row: the row is the attacking type, the column is the defending type. Blank means normal damage. Dual types multiply, so Water against a Rock/Ground Pokemon such as Geodude or Rhyhorn is ×4.

Attacker \ Defender	Nor	Fir	Wat	Ele	Gra	Ice	Fig	Poi	Gro	Fly	Psy	Bug	Roc	Gho	Dra
Normal													×½	×0
Fire		×½	×½		×2	×2						×2	×½		×½
Water		×2	×½		×½				×2				×2		×½
Electric			×2	×½	×½				×0	×2					×½
Grass		×½	×2		×½			×½	×2	×½		×½	×2		×½
Ice			×½		×2	×½			×2	×2					×2
Fighting	×2					×2		×½		×½	×½	×½	×2	×0
Poison					×2			×½	×½			×2	×½	×½
Ground		×2		×2	×½			×2		×0		×½	×2
Flying				×½	×2		×2					×2	×½
Psychic							×2	×2			×½
Bug		×½			×2		×½	×2		×½	×2			×½
Rock		×2				×2	×½		×½	×2		×2
Ghost	×0										×0			×2
Dragon															×2

Key: ×2 super effective · ×½ not very effective · ×0 no effect.

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.