Happiness is on a scale of 1-255, and happiness evolutions happen at 220.
When you catch a pokemon it's probably around 70-80.
Wearing a Soothe Bell adds 1 to all of these:
Gaining a level is 2 happiness (6 if you caught it in a luxury ball)
Walking 256 steps is 1 happiness (2 if in a luxury ball)
Using a stat modifier item on it is 2 happiness (6 for luxury ball)
Soothe Bell has no effect on these:
Energypowder is -5 happiness
Heal powder is -5
Energy root is -10
Revival Herb is -15
XI Wiki

