|This article is about an older version of DF.|
How "big" the creature is, measured in cubic centimeters (which is roughly equal to one gram of mass for normal body materials). Bodysize determines what kind of equipment a creature can wear, how much damage they can absorb, how much damage they can inflict in melee and how much is yielded from butchering. Size is inherited through the genetics system.
The average size set for a dwarf is 3000, 15000, 60000, being the sizes as a baby, child and adult respectively. Modified with height (short to tall) and broadness (thin to fat).
Also, Size for items is also in centimeters cubed and (with material) determines the weight of items (e.g. iron mace weighs ~ 6.2kg, copper halberd ~ 10.7kg etc.) and, therefore determines inflicted damage.
Changing this too much can lead to fun.