HELP Specifying a number of Circles to be randomly populate a grid

I need HELP please,

I have a grid which is populated with various sizes of circles. I want to be able to set a maximum limit on the number of each circle size.

Does anyone know how?

For example

Max Circle size 3 = limit of 25

max circle size 6 = limit of 12

max circle size 12 = limit of 10

max circle size 18 = limit of 6