For a full IV ranking by species, use third-party tools like PvPoke.com. The math:
Stat Product = the new IV rating
In Great League and Ultra League, the best Pokémon isn't the one with the highest IVs — it's the one with the highest stat product (Atk × Def × HP) at the highest level allowed under the CP cap.
Why? Because lower Atk IVs reduce CP, which lets the Pokémon reach a higher level (and therefore higher Def and HP) before hitting the cap. The optimal spread is often 0/15/15 or 1/15/15 — surprisingly low attack.
Example: Azumarill in Great League
- 15/15/15 IVs: reaches Level 38.5, stat product ~1,789, rank #4096
- 0/15/15 IVs: reaches Level 50, stat product ~2,127, rank #1 (the "best" Azumarill in Great League)
- Difference: ~18% more bulk + Atk for the lower-IV version
How to use rank %
PvPoke.com ranks every IV combination from 1 to 4096. A 90%+ rank is "good enough" for casual play; 99%+ for serious GO Battle League. Lucky Pokémon (12-15 IV floor) cap out around 50% rank max — bad for Great League, fine for Master League.
When 15/15/15 is best
In Master League (no CP cap), 15/15/15 always wins because there's no penalty for high Atk. In Premier Cup variants (no legendary), same logic. Always Hundo for Master, almost never Hundo for Great/Ultra.