Shelving fails in two ways: it sags, or it tips. Both are avoidable and neither is about paying more.
What a load limit means
A stated limit is for weight spread evenly across the shelf, not concentrated at one end. Where a supplier gives a figure we list it; where none is given we say so rather than invent one.
Distribute weight downward
Heaviest items on the bottom tier, lightest at the top. A tall unit loaded top-heavy is unstable even against a wall.
Anchor it
Any unit taller than it is wide should be anchored, and that is not optional in a home with children. Use a fixing suited to the wall — the bracket in the box is half the job.
Level the feet
Floors are rarely flat. Two minutes with the adjusters removes wobble and stops a stacked unit walking across the tiles.
Stackable sets
Stackable cubes and countertop shelves state how many tiers they are rated for. Going one higher is where most failures start.