Definitive Guide to Ball Sizes

From left two right (two of each): Tiny, Mini Hollow, Medium, Regular

Tiny

1 1/2" diameter, solid foam, weighs under one ounce. Usually from keychains

Mini Hollow

1 13/16" diameter, hollow, weigh 1 ounce. Usually found as part of games, no readily available source.

Medium

1 7/8" to 2" diameter, solid foam in two densities: one rather hard, one slighlty softer, weighs two ounces. Sources: Omaha Vaccine, Pet Food Warehouse, etc.

Regular

Regular sized tennis balls, weighs about two ounces.