How to choose correct flauges size.

Avie • Momma of 2 beautiful boys. 9/13/12 , 8/6/18. 💙💙💙💙💙💙 and a loving wife 8/23/14 ❤❤❤❤

So when i pump i get like 1-1 1/2 oz combine. And i seen this today and clearly mine are to big. But i have no clue how to choose the correct size. :( makes me feel dumb. But for so long i have been so sad that i cant pump enough for my lo. When i go to work. Until i found this out. Help plz!