You open the cabinet under the sink and you are looking at a front row. One row. Everything else is behind it in the dark, and finding anything means pulling that front row onto the floor first. That is how you end up with two bottles of the same cleaner. The second got bought while the first sat at the back.

Depth under a sink is worse than depth anywhere else in the house. The opening is narrow, the shelf is deep, and a drain pipe runs down the middle. So you go in at an angle with one arm and pull out whatever your hand closes on. What sits at the back does not get used. It gets stored.

These slide. The tier comes out to you instead of you going in after it, and once it is out you are looking down at a whole shelf from standing height. Nothing is behind anything. That matters more than it sounds. The problem was never space. You had space. You could not see it.

The second tier does the other half of the job. The waste under a sink is vertical: empty air stacked above short bottles. A shelf across the top of them turns that air into floor. And you get two, which matters, because the pipe cuts that cabinet into two zones. You are not organizing one space. You are organizing two narrow ones that share a door.

Here is what people get wrong buying these. They measure the cabinet and forget the plumbing. What decides it is the clear run of floor on each side of the drain pipe, not the width of the door. And anything you stand upright now, a jug, a tall spray bottle, stops fitting the moment a shelf sits above it. Those go on the top tier, or somewhere else.

You do get more shelf out of this. That is not the part you notice. What you notice is that nothing is hidden behind anything anymore, so you stop buying the second bottle. If the back of that cabinet is where things go to be forgotten, that is what this fixes.