I was trying to determine what the "acceptable" size bulbs should be when purchasing?
I saw an ad which stated the bulbs were 14/16 cm. Is that considered a large, medium or small?

What kind of lily were they advertising? Some lilies produce small bulbs naturally and others will grow quite large.

Oriental Lily

14 to 16 cm is acceptable size and its generally the standard number retailers use. Bulbs will be at least that size or larger even tho they list them as 14 to 16 cm. Trumpet lily bulbs, by nature are larger and you might see them listed as 18/20 or 20+ cm. To me, the quality of the bulb is more important than size--how solid and tight the scales are, how heavy, how fresh, etc.

Thanks for the information. I should have thought of this previously to compare bulbs I am getting this spring.
When you state "heavy", what does that refer to? More weight means a more solid bulb? Like firmness?

Yep. They're not dried out or dehydrated; they're fresh, make sure theyre not rubbery and they do not have loose scales.

Tightness of the bulb scales may not be a good indicator for all species bulbs, but it can be true for all hybrid and species asiatics, trumpets and orientals. "Tightness" as I see it, is how solid the bulb is. A bulb that is like a solid ball, with now air spaces between scales, is the epitome of "tight".

IMO, more important is Lorn's mention of bulb firmness (in its individual parts, not necessarily as a whole). This hold true for any lily bulb. Some species bulbs (and their hybrids) are naturally loose growing, but a good quality, fresh bulb will always be firm and turgid.