Instructions
Calculate the spell coefficient of a specific direct healing spell by dividing the cast time by 3.5. Multiple this result by 1.88. Calculate the spell coefficient of a "heal over time" spell by dividing the spell's duration by 15 and multiplying the result by 1.88.
Press "C" to bring up your character window. Look down your list of bonuses until you find the spell section. Find the result labeled "Spell Damage." The spell damage stat increases your healing power so your heals are more effective, whether they are direct or heal over time spells.
Multiply your spell damage number by the coefficient calculation for a specific spell. Open your spell book and add this number to the base minimum and maximum healing numbers for the spell. That is the healing power range you receive, given that specific spell and your current equipment.