A creature's size can fall into one of the 9 categories (from smallest to largest):
- Fine
- Diminutive
- Tiny
- Small
- Medium
- Large
- Huge
- Gargantuan
- Colossal
A creature's size gives it certain bonuses and penalties in combat. Most playable races are medium, except goblins, gnomes and halflings, who are small.
The special size modifiers for both defense and attack (including Combat Maneuver Bonus and Combat Maneuver Defense) are as follows:
- Fine +8
- Diminutive +4
- Tiny +2
- Small +1
- Medium 0
- Large -1
- Huge -2
- Gargantuan -4
- Colossal -8
Generally, larger creature means stronger, slower and more easier to hit creature. And vice versa: the smaller a creature is, the more dexterous, but weaker it is.
A number of special abilities (spriggan's Size Alteration, druid's Wild Shape) and spells can reduce or enlarge a character, changing their size and giving appropriate bonuses and penalties. Most notable examples are first level arcane spells Reduce Person and Enlarge Person to decrease and increase one's size by one category (medium character enlarges to large and reduces to small).
Enlarged characters take up more space which is not relevant to gameplay unless you try to squeeze a number of large creatures into a narrow passageway of a dungeon. They also have their reach of melee attacks increased which is very important since it allows to attack from behind the backs of their more "tanky" companions and to hit more creatures without moving (thus more full attacks and more effective Cleave and Great Cleave).
Spells that change size usually apply specific modifications to character's ability scores. Enlarge Person gives a +2 size bonus to Strength and a -2 size penalty to Dexterity in addition to size modifiers appropriate for a new size. Characters enlarged by this spell retain their attack bonus (+1 bonus to attack rolls from higher Strength, but -1 penalty on attack rolls due to increased size), but have worse AC (-1 penalty from lower Dexterity and -1 penalty due to increased size). Reduce Person affects characters in a similar way, but gives great benefits to melee attackers that use Weapon Finesse feat with appropriate weapons and to ranged attackers (including casters): they get +2 attack bonus (+1 from higher Dexterity and +1 due to reduced size) and +2 AC bonus (again, +1 from higher Dexterity and +1 due to reduced size).
Size changes do not stack (in this game the characters change their size from initial every time a new size-changing spell was cast on them), but effects from magical size changing are (unless they give bonuses of the same type, as a general rule). Enlarge Person and Reduce Person do in fact dispel each other.
| Spell | Size change |
|---|---|
| Reduce Person | decrease by 1 category |
| Enlarge Person | increase by 1 category |
| Righteous Might | increase by 1 category |
| Frightful Aspect | increase by 1 category |
| Legendary Proportions | increase by 2 categories |
Since melee and ranged weapons increase (or decrease) in size with their owner, they deal more (or less) damage. Damage from spells and alchemist bombs doesn't depend on the attacker's size. Bonus to damage from weapon's actual size stacks with bonus from effective size change of a weapon ("as if one size larger than it actually is" and the like), be it a spell effect (Lead Blades and Hurricane Bow) or a weapon specifics (Bashing Shield).