The Size of a unit determines how many Supplies they consume each turn. In previous games, this was internally known as Supply Size.

To see a unit's supply usage, one can simply click on "Size" on their stat sheet. For a quick and click-less calculation, though:

• Take their Size.
• If their Size is greater than 1, subtract 1.
• If they're a Glutton, add their amount of Gluttony. (They eat much more than similar beings.)
• Divide the result by 2.
• If they're an Animal, divide the result by 2 again.
• Round the result up to this point down to the nearest 0.5 (0.75 becomes 0.5, for instance, and 0.25 becomes zero).
• If the result up to this point is less than zero, make it zero.
• If they have a Supply Bonus, subtract it from their supply usage. (They give into the larder.)

Yes, the manual is wrong about this. You're not crazy. It's right about Animals eating less, however. For a non-Animal without any Gluttony, here's how Supply usage relates to size:

A Glutton who Needs not Eat will still eat; they just won't get Diseased from Starving. For those with the "Need not Eat" trait and not the Gluttony trait, their supply usage before their Supply Bonus is zero.