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

Rhydon
Rhydon 		Base
stats		 Stats Effort Possible genes (IVs)
Level
HP 105
316–347
31
Attack 130
262–293
31
Defense 120
242–273
31
Special Attack 45
94–124
31
Special Defense 45
94–124
31
Speed 40
84–114
31

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

This Rhydon'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