An attack roll determines if you hit a target. Different attacks pit different abilities and defenses against each other. Depending on the power you attack with, you may perform a Strength vs AC attack, or Wisdom vs Fortitude. Some attacks hit multiple targets, while others only target one but may make multiple attack rolls against the same target.
The basic formula for an attack roll is as follows:
- Roll a d20.
- Add 1/2 your level (rounded DOWN).
- Add the applicable ability modifier. The power you use determines which ability applies.
- Add any bonuses that affect the attack roll, such as feat, power, proficiency, or situational bonuses. This may also include the enhancement bonus on your weapon or implement.
Now compare your result to the defense the power targets (AC, Reflex, etc). If your roll is higher than or equal to the defense score, you hit and whatever effects the power specifies take effect (often a damage roll). Otherwise you miss, which may still have effects (such as half damage).