Size
Creatures larger or smaller than medium-size get the following adjustments listed below.
SIZES
Most adult humans are size 5 (aka "medium-sized") standing at least 4 feet tall and under 8 feet tall. They occupy roughly a 5 x 5 x 5 foot cube of space and can reach everything within their space or within their reach. Every size lower is roughly half as big while every size larger is roughly 50% bigger than the previous size. (Size2)/5 = space in feet (space x space x space).
SIZE 6 (LARGE)
+2 size bonus to...
- Strength score
- Parry DC
- Fortitude saving throws
- Brawn skill modifier
- +1 base weapon damage die (see Weapon Sizes)
-2 size penalty to...
*For each size larger, you stack these adjustments. So it would be +4/-4 for Size 7 (Huge), +6/-6 for Size 8 (Gargantuan), +8/-8 for Size 9 (Colossal), etc.
SIZE 4 (SMALL)
+2 size bonus to...
-2 size penalty to...
*For each size smaller, you stack these adjustments. So it would be +4/-4 for Size 3 (Tiny), +6/-6 for Size 2 (Diminutive), +8/-8 for Size 1 (Fine), etc.
ACTIONS
If a creature is two sizes larger or smaller than you, you...
- cannot flank them
- cannot gain high ground bonuses against them
- cannot take attacks of opportunity against them
- can move through their space without having to overrun them, treating it as difficult terrain*
Creatures with the Blobular shape or Amorphous ability are an exception. They can make attacks of opportunity against creatures of any size smaller and prevent smaller creatures from moving through their space.
*If the creature is 2 sizes smaller than you or smaller, doing this imposes a trampling hazard on the creature (Reflex DC10 + your Brawn modifier or they take damage as if struck by your unarmed strike or slam attack, whichever is worse). If you move normally, they have advantage on this save. If you intentionally try to trample them, they don't have advantage but you move at half speed.
CARRYING CAPACITY
A bipedal creature can carry less or more weight depending on its size category: Fine x1/16, Diminutive x1/8, Tiny x1/4, Small x1/2, Medium x1, Large x2, Huge x4, Gargantuan x8, Colossal x16.
Quadrupeds: Fine x3/32, Diminutive x3/16, Tiny x3/8, Small x3/4, Medium x1.5, Large x3, Huge x6, Gargantuan x12, Colossal x24.
RAGDOLLING
If you pin a creature that is more than 1 size smaller than you, you can use them as an improvised melee or thrown weapon. The damage dealt is based on the victim's size as an object and the wielder's Strength modifier. The victim and the target share the damage dealt 50/50. A grappled creature or swallowed creature cannot suffer this humiliation, only one that remains pinned.
CLIMBING CREATURES
It’s possible to climb a creature that's two sizes larger than you or larger treating their Parry DC as the Climb DC. If successful, you add your weight to the creature's carrying load and move upwards the appropriate distance. While climbing a creature, you are treated as flanking it for the purposes of weapon attacks you make against it despite the size difference.
MASSIVE
Some colossal creatures and objects have the massive trait. Such creatures are treated as terrain rather than an actual creature by most smaller creatures. They are immune to damage dealt by weapons that are not area of effects. Siege weapons and massive spells are needed to even scratch such behemoths. For simplicity's sake, treat creatures with this trait as if they were one size larger than colossal.
TARGET CREATURES
Spells and other effects that target 2 or more limited number of creatures or objects are assumed to target medium-sized ones unless noted otherwise. If the spell lifts, moves, grants or adjusts base speeds, or transports targets, assume it can include 4 small targets instead of one medium target, 16 tiny per medium, 64 diminutive per medium, and 256 fine per medium. In reverse it can affect 1 large target per 4 medium targets, 1 huge per 16 medium, 1 gargantuan per 64 medium, and 1 colossal per 256 medium. Effects that target "self", "personal", or only 1 creature, have no size limitation. Instead of targeting objects, you can target a single 5-foot space per medium target and affect a wall, ceiling, or floor (if possible).
REACH
Reach is the maximum distance at which you can physically affect a target through direct contact. This includes contact made with your body or a held object (such as a weapon), but excludes any effect that does not require physical contact (such as projectiles, rays, or emanations). Non-contact effects (such as ranged Strikes, spells, or energy attacks) never use Reach.
NATURAL REACH
Natural Reach is the distance you can physically touch using your body alone, without tools or weapons. This typically reflects your size and anatomy. For most creatures, their natural reach is equal to half their size -1 (rounded down, minimum 0). This includes unarmed strikes and other innate weapons, touch-based effects, and abilities requiring direct bodily contact.
FULL REACH
Full Reach is your Natural Reach plus any extension provided by held items, such as weapons with the reach trait. This is the default reach for most melee attacks.
THREATENED REACH
Threatened Reach is the area within which you can react to enemies, such as making Attacks of Opportunity or triggering reactions tied to your reach. By default, your threatened reach is always equal to your innate reach, unless you wield a reach weapon you are proficient with.
WEAPON SIZES
Ignore the normal size adjustments for weapon damage dice from the weapons table for small and large weapons and from Improved Natural Attack and similar effects. Weapons designed for Medium and smaller characters deal their normal weapon damage dice as medium creatures. Weapons designed for Large and larger creatures deal +1 base damage die per size larger.
For example, a longsword is normally 1d8 so a large longsword would be 2d8 and a huge longsword would be 3d8 and a gargantuan longsword would be 4d8 and so forth. A greatsword is normally 2d6 so a large greatsword would be 4d6, a huge greatsword would be 6d6, a gargantuan greatsword would be 8d6 and so forth.
Improved Natural Attack (Feat): Replaced with the Weapon Focus feat.
Unarmed Strike (Monk class feature): Replaced with the Weapon Focus (Unarmed Strike) feat that automatically increases in tier so that it's always half your monk level, rounded up.
Critical Hits and Vital Strike: Critical hits multiply weapon damage dice normally, but Vital Strike and similar effects do not. Vital Strike adds only the base weapon's base damage dice, not additional damage dice added for being larger. So a Vital Strike with a large greatsword would be 6d6 and an Improved Vital Strike with a large greatsword would be 8d6 and a Greater Vital Strike with a large greatsword would be 10d6. Vital strike with a large longsword would be 3d8, Improved Vital Strike with a large longsword would be 4d8, and Greater Vital Strike with a large longsword would be 5d8.