Measured fit, not a generic book count
Will this item, box or binder actually fit?
Compare three measured dimensions, test allowed rotations, and see the failed dimension or remaining clearance. No catalog, title, barcode or patron data is needed.
Item
Usable opening
Orientation
Measure the clear opening and usable depth, not the outside furniture dimensions.
Measure the opening, not the furniture
Use the clear space between uprights, the space above the shelf surface, and the usable depth before a back panel or obstruction. Subtract any clearance your handling policy requires before entering the opening dimensions. An exact dimensional fit leaves no removal gap.
The item is treated as a rectangular bounding box. Rotation only tests geometry; it is not a recommendation to store fragile books, binders or archival materials in a particular orientation.
A binder that fails upright can fit sideways
A measured item 32 × 29 × 6 cm does not fit upright in an opening 30 × 35 × 25 cm: its width exceeds the opening by 2 cm. If rotation is allowed, the 29 × 32 × 6 cm orientation leaves 1 cm of width, 3 cm of height and 19 cm of depth. Use your own measurements rather than treating this example as a standard binder size.