The box didn't fit the closet. Usually it's how we measured
You buy a storage box, get it home, and it won't go into the closet. We hear this a few times a month. Most of the time it isn't the box, it's the order in which things got measured.
Measure the inside. In a conventional Japanese closet the opening is roughly 1,600 to 1,800 mm wide, 800 to 900 mm deep and 1,800 mm high, but the older the building the more those numbers drift. Two rooms in the same house can differ. Keep the tape against the inside face: posts stick out, the beam drops, and the sliding-door track steals a few centimetres.
Then subtract. A 1,800 mm space takes seven 240 mm boxes if you stack them flat, but the top one needs a step stool. Plan on five or six being what you can actually reach. Two rows of 450 mm boxes fit a 900 mm closet, and the back row will be annoying. Put everyday things in front and seasonal things behind, and it stays workable.
Shape matters too. You reach into a closet from above, so a drawer you pull toward you beats a lid you lift. Our Drawer Box 45 is 330 by 450 by 240 mm and holds 5 kg per tier. It's clear, so you stop dragging everything out to see what's inside.
Last thing, moisture. Closets tend to sit against an outside wall and collect condensation in the rainy season. Even with a well-sealed box, empty it once or twice a year and keep a dehumidifier in there.
