This damage calculator requires you three things to show the result. They are Intellect, Magic and foe's Defense.

The damage settles near the upper limit of the random number range (10%). If the damage is at 500, the actual value takes somewhere in a range of 450-500.

Power is additive to attack power, so it can be said it becomes less valuable relative to the later stages of the game.

Foe's defense is defaulted to 150. This is the average defense of the last dungeon's enemies.

The item "Full Moon" is exclusive to the Full Moon Queen. Other than periods of full moon, damage is halved (It doesn't mean power halves).

Loyalty is an item for magic, such as Loyal Fire, whose power relatedly changes with loyalty. The power is halved for every 1 loyalty level decrease (not damage).

Skills that depend on HP percentage, such as Roma Calor, have a separate formula to calculate. You can calculate theose damages in each magic's page.