I think making a best guess is what you have to do...precise as possible but you have to use common sense too.

No, garlic cloves can be all sizes as you mentioned, some are tiny while others are very large. I grow the Music type here, and they do quite well and are always single layers and quite big cloves. They are a hard neck variety that is planted in fall and is harvested the following early summer. There is a scape that also needs to be cut off once they show up. These scapes take necessary nutrients from the bulbs. Depending on a recipe, garlic, like salt can be as much, or as little as you prefer. Most store bought are soft neck and do have many sizes in a single bulb. Check out elephant garlic. Milder, with huge cloves!

Of course elephant garlic is actually not garlic at all but a garlic flavored leek. All the same, a clove the size of a baseball is a bit much I think.

Actually the whole elephant garlic is about the size of a baseball, not a single clove. They are quite mild in any case. I tried growing many garlic types in the past, and was very impressed with Music. Right now, they are not being sold for growing as its past their planting time, which is the fall. Orders for Music will be accepted starting about Mid May to June, for fall planting. I add bone meal to my garlic trench prior to planting the individual cloves. My Music from this past summer garlic is now getting to a brown spot stage, so I must think about removing the skins and either pickling it, or chop and freeze it. Have about 15 whole bulbs left. This year, I hope to also have some decent shallots. The type I am growing are bigger than golf balls, and are next to the garlic.