How are Tulips measured?
Tulips are measured by the circumference of the bulb. The greater the circumference of the bulb, the more food can be stored by the plant to give it a better start and greater success.
A larger Tulip bulb will produce a fuller plant with stronger stems and bigger flowers giving you a more beautiful garden. A 12+ cm Tulip will produce 2-3 stems per bulb versus a smaller bulb size.