Depth decides what fits
Height gets the attention and depth does the work. Around 10 to 12 inches of depth holds hardbacks and boxed items. Under about 8 inches you are limited to paperbacks and decorative objects, which is fine if that was the plan and a problem if it was not.
Measure the tallest thing you own
Fixed shelves are set at a chosen spacing and that spacing is the real specification. Adjustable shelves solve this, so if you own tall art books or file boxes, check whether the shelves move before you check anything else.
Check the weight capacity per shelf
Books are heavier than almost anything else people put on shelves. Per-shelf capacity is listed in the specifications on every product page here, and a shelf rated for light decorative use will bow under a full run of hardbacks.
Open, closed, or both
Open shelving makes a room feel larger and makes clutter visible. Closed doors do the reverse. A piece with open upper shelves and closed lower cabinets is the compromise most rooms actually want, because the mess collects at the bottom anyway.
Before it goes against the wall
- Anchor anything tall. Tip-over hardware ships with most tall pieces and is listed in the specifications when it does.
- Check the baseboard. A bookcase with a flat back sits proud of the wall by the depth of your baseboard unless it has a recessed toe or you notch it.
- Leave the top shelf reachable. Storage above your own reach becomes storage you never use.