Each of a creature’s abilities has a score, a number that defines the magnitude of that ability. An ability score is not just a measure of innate capabilities, but also encompasses a creature’s training and competence in activities related to that ability.
A score of 10 or 11 is the normal human average, but adventurers and many monsters are a cut above average in most abilities. A score of 18 is the highest that a person usually reaches. Adventurers can have scores as high as 20, and monsters and divine beings can have scores as high as 30.
Each ability also has a modifier, derived from the score and ranging from −5 (for an ability score of 1) to +10 (for a score of 30). The Ability Scores and Modifiers table notes the ability modifiers for the range of possible ability scores, from 1 to 30.
Ability Scores and Modifiers
To determine an ability modifier without consulting the table, subtract 10 from the ability score and then divide the total by 2 (round down).
Because ability modifiers affect almost every attack roll, ability check, and saving throw, ability modifiers come up in play more often than their associated scores.