Reference

How much weight can a shelf hold?

The short version: it depends on the shelf's width, material, and thickness, and the risk is sagging, not snapping. As a guide, in 18 mm MDF, 30 cm deep, the builder adds a center support from 48 cm of width for everyday use, and from 40 cm for a heavy load; a stiffer material or a thicker board goes further before it needs one.

Figures for France, where 18 mm MDF is on sale. Your country may stock different boards, and the builder tells you which spans yours allow.

What “light”, “medium”, and “heavy” mean

Load is measured per metre of shelf. Here is what each level looks like:

Load level	Weight per metre	Example
Light	about 10 kg/m	decorative items, a few light objects
Medium	about 30 kg/m	a normal row of books
Heavy	about 60 kg/m	packed books, records, tools

So an 80 cm shelf holds roughly 8 kg at a light load, 24 kg at medium, and 48 kg at heavy, as long as the shelf is stiff enough not to sag.

Why width and material decide the limit

A shelf rarely breaks; it bows over time. The wider the shelf and the weaker the material, the less weight it holds before it sags.

Pine is about three times as stiff as plywood or MDF, so it holds far more weight for the same width. Compare MDF, plywood and pine
In 18 mm MDF, 30 cm deep, the builder adds a center support from 48 cm of width for everyday use, and from 40 cm for a heavy load; a stiffer board goes further before it needs one. See standard shelf dimensions

The rule of thumb

If your shelf is wide or the load is heavy, do one of these: shorten the span, add a center support, use pine, or move to a thicker board. Any one of them buys you more weight before the shelf sags.

How Kamba works it out

Kamba does not guess. For your exact width, material, thickness, and expected load, it calculates the deflection and compares it to a limit set well under a visible sag. If your design exceeds that limit, Kamba tells you and recommends a fix.