Instructions
Press start and select "Pokémon" from the menu. Select the Pokémon you wish to evaluate and select "Info."
Enter the stats into the IV calculator at http://www.serebii.net/games/iv-calcdp.shtml
to determine your Pokémon's individual stat values.
Determine whether the IV's are odd or even. This will help determine the hidden power value. Start with the the value 0. If the HP value is odd, add 1 to the hidden power value. If not, add nothing. If the Attack value is odd, add 2. If not, add nothing. If the Defense value is odd, add 4. If not, add nothing. If the Speed value is odd, add 8. If not, add nothing. If the Special Attack value is odd, add 16. If not, add nothing. If the Special Defense value is odd, add 32. If not, add nothing.
Multiply the hidden power value by 15 and then divide it by 63. If there are any decimals after the first digit, truncate them. The resulting value is your hidden value type. Compare the value to the table at http://www.serebii.net/games/hidden-power.shtml.