About this tool
The Pokémon Type Effectiveness Calculator tells you exactly how much damage an attacking move type deals to a defending Pokémon based on its typing. Pick the attacking type and the defender's one or two types, and it multiplies the two matchups together to give the final damage multiplier — 0× (no effect), 0.25×, 0.5×, 1×, 2×, or 4×. Everything runs in your browser using the full 18-type chart; nothing is uploaded.
The multiplier comes from the standard Generation VI+ type chart covering Normal, Fire, Water, Electric, Grass, Ice, Fighting, Poison, Ground, Flying, Psychic, Bug, Rock, Ghost, Dragon, Dark, Steel, and Fairy. Each cell is 0 (immune), 0.5 (not very effective), 1 (neutral), or 2 (super effective). For a dual-type defender the final multiplier is chart[attack][type1] × chart[attack][type2], so a move that is 2× against both types lands a 4× hit, while one that is 0.5× against each is resisted to 0.25×, and any single immunity zeroes the whole thing.
Below the headline result the tool builds a full defensive summary: it runs every one of the 18 attacking types against the chosen defensive typing and lists the 4× and 2× weaknesses, the ½× and ¼× resistances, and any complete immunities. That makes it a quick way to scout what a given Pokémon (or team slot) is weak to before building around it.