Pokémon Gen 1 Catch Rate Calculator
Common (Pidgey, Rattata, Caterpie) – 255
Semi-Common (Pikachu, Jigglypuff) – 190
Uncommon (Ekans, Sandshrew) – 120
Rare (Vulpix, Meowth) – 90
Very Rare (Dratini, Eevee) – 75
Evolution Stage 1 (Pidgeotto) – 60
Starters & Safaris (Bulbasaur, Scyther) – 45
Evolved Forms (Pidgeot, Arcanine) – 30
Ultra Rare (Snorlax, Dragonair) – 25
Legendaries (Mewtwo, Articuno, Zapdos, Moltres) – 3
Poké Ball
Great Ball
Ultra Ball
Master Ball
None
Asleep / Frozen
Paralyzed / Burned / Poisoned
Catch Probability
0%
Understanding Generation 1 Catch Mechanics
In the original Pokémon Red, Blue, and Yellow games (Gen 1), the catch mechanics were significantly different—and more "glitchy"—than in modern games. The system relies on a series of random checks (0-255) against the Pokémon's base catch rate, its current health, and its status condition.
The Three Checks of Gen 1
Unlike later games that use a single complex formula, Gen 1 processes the catch in specific steps:
- Status Check: If the Pokémon is Asleep or Frozen, there is roughly a 10% (25/256) chance of an instant catch. If it is Paralyzed, Burned, or Poisoned, that chance is roughly 5% (12/256).
- Ball/Species Check: If the status check fails, the game checks if a random number (0-255) is less than the Pokémon's base catch rate. If you use a Great Ball, this check is slightly easier.
- HP Check: Finally, the game factors in the current HP. Due to an infamous oversight in the Gen 1 code, using an Ultra Ball is actually less effective than a Great Ball in very specific low-HP scenarios, though generally, the Ultra Ball remains superior for high-level targets.
Catch Rates for Kanto Legendaries
Legendary Pokémon like Mewtwo, Articuno, Zapdos, and Moltres have a base catch rate of 3. This is the lowest possible value, making them extremely difficult to catch without a Master Ball.
| Pokemon | Base Catch Rate |
|---|---|
| Mewtwo / Birds | 3 |
| Snorlax | 25 |
| Starter Pokémon | 45 |
| Abra | 200 |
| Magikarp / Pidgey | 255 |
Pro Tips for Catching in Red/Blue/Yellow
- Always use Sleep: Sleep is the most powerful modifier in Gen 1. It provides a flat chance to bypass all other HP requirements.
- False Swipe doesn't exist: You must carefully lower HP without knocking the target out. Aim for roughly 10-20% HP.
- The Great Ball Glitch: In some instances, because the Great Ball uses a divisor of 8 and the Ultra Ball uses 12 in the HP calculation, the Great Ball can actually be more effective for specific mid-range HP targets.