hand rule
The standard against which optimal breast size is gauged in seeking a suitable mate, etc.

The optimal breast size is equal to the amount that can be fit in one's hand; any less is not enough and any more is excessive, wasteful, and unnecessary.

The curve follows a sharp Gaussian/Cauchy–Lorentz function and distribution.

f (x; 0,1) = 1 / π (1 + π^2)

This is also known as the Breast-Volarity curve.
Person 1: Wow, she has exquisite breasts.

Person 2: Eh, they're too large.

Person 1: Nonsense!

Person 2: Don't forget the Hand Rule.
Person 1: Ahhh, good call.