Under-bed height changes across the frame. Rails, bolts, slats, center supports, floor variation, and mattress load can all create a lower point than the easy measurement at one corner.
Find the lowest point
Measure from the floor to the bottom of side rails, center beams, slats, brackets, bolts, and sagging upholstery. Check the intended entry side and the full path to the final position.
Use full container height
Include lid rims, zipper seams, handles, wheels, and any bulge when the container is filled. Leave a small practical margin so the bin does not scrape or snag every time it moves.
Measure pull-out room
The open floor beside the bed must be at least long enough for the container to exit and turn as needed. Nightstands, walls, doors, rugs, and nearby furniture can trap a bin that fits perfectly underneath.
Choose access frequency
Rolling rigid bins suit frequent use when flooring allows it. Fabric bags are lighter and can fit shallow gaps but may be harder to slide when heavily packed. Long divided containers can organize more but require more pull-out space.
Protect the items and the room
Match dust, moisture, pest, and crush protection to the contents. Avoid blocking floor vents or mechanisms, stay within bed-frame instructions, and lift safely rather than overloading one very large container.