The size of a character is how the game represents the height of the character and somewhat the width. The size of a human character is 1. It is roughly 6ft or 2 yds. All human characters or man sized character will be considered Size 1. Everything is not perfect but it gives an rough idea. There can be character smaller and they will be considered a size 0. Size 0 characters will not occupy a square.
A square is an area a character takes up in combat. The amount of squares a character takes up is the same number as there size. So if a character has a square of 1 it will take up one space. A character with a size of 0 will be treated as if it takes up 1 square. A character with a size of two will wake up a 2×2 area.
A characters natural reach is also compared to size. A character of size one will have a natural reach of one meaning they can attack the next square over from them naturally. A larger character however will be able to attack from there size.
This rule only applies to characters larger than 3. In a 3×3 square the middle square would be considered on occupied square. I can most easily show this with a 4×4 square which has a 2×2 occupied square at its center. This area is considered occupied. The occupied square cannot pass through solid objects and cannot turn unless the area of its size is free. Any character with an occupied square does not get a free spin.
Sharing A Square
Two characters can share the same square. You cannot however share an occupied square. Characters of size 2 cannot overlap but can share 2 squares.