3" wide. The shelves have 1" usable space inside (height). Shown with these bottles for scale (left to right): Mini Mason Jar - Large, one of the 12 Tiny Glass Bottles (sans cork), Large Clear Resin Potions Bottle, one of the Amber Even Tinier Bottles. Also shown in a Small Frame Shadowbox for size.
Note: this item will come shipped in a flat sheet: almost completely cut out, save a tiny (1/8") spot that you can snip with scissors or a sharp blade. Keeps all the pointy details from being banged up during transit.
Design Team Member Nichola Battilana made The Collector's Room Box (see the wide photo below). More info in the blog and/or see the supply list.