WHIRLWIND EXPLANATION: Pokémon have a fixed, permanent score from 0 to 31 for each stat that affects how good that stat can ever get.

This calculator will figure out that score (called a "gene" or, more obtusely, an "IV") for you, so you can discard the unworthy. It's more accurate for higher-level Pokémon, so it's helpful to go into a level 100 wifi battle with someone and check your Pokémon's stats from there.

Stat calculator

Aggron
Aggron 		Base
stats		 Stats Effort Possible genes (IVs)
Level
HP 70
247–278
31
Attack 110
222–253
31
Defense 180
361–392
31
Special Attack 60
123–154
31
Special Defense 60
123–154
31
Speed 50
104–134
31

Congratulations, you've narrowed your Pokémon's stats down exactly!

This Aggron's Hidden Power inflicts Dark damage, with 70 power.

And for your copy/pasting pleasure:

31 HP; 31/31 Physical; 31/31 Special; 31 Speed

or start over