I go by weights as well.

It seems everyone has different ideas if I ask by size. One supplier's small rats may be twice the size of another's smalls.

If I stick to weights, everyone can give me what I need, regardless of what they call it.

For me, " weaned" rats weigh between 30 and 40 grams. "Small" rats go between 50 and 75 grams. "Medium" rats, and I only have one female who eats them, go between 125 and 175 grams.

Gale