Measure the top of the machine to the bottom of the base that sits on the table. The size of the Globe can be determined by the size of the Gumball Bank. If your Gumball Bank is on a stand you will need a 15” Glass Globe.
If you’re just not that convinced that you measured it correctly then call the customer service staff at Candymachines.com. They will happily help you with all your Gumball and Candy Machine questions.