Binder spines are always wider than ring diameter.

This is the number one point of confusion for people shopping for binders. The office products industry defines binders based on the ring size, not on the width of the binder spine. 

Ring Size Spine Width Aprox. Sheets *
1/2" Recycled Binder  |  Select
.75" W 100
All 1" Recycled Binders Original | Select  |  Professional
1.56" W 218
All 1.5" Recycled Binders  |  Original  |  Select  |  Professional 2.25" W 300
All 2" Recycled Binders  |  Original  |  Select  |  Professional 3" W 437
All 3" Recycled Binders  |  Original  |  Select  |  Professional 3.875" W 560
All 4" Recycled Binders  |  Select  |  Professional 4.69" W 690

* Note: The number of pages that can fit in a binder varies considerably based on the weight of paper used. The numbers above reflect our tests with a 20 lb paper, but keep in mind that even 20 lb paper varies a bit between manufacturers.