Weight ratings explained: what garage storage can really hold

What a rating actually describes

A load rating on a shelf, a hook or a rack is a statement about the product, made by its manufacturer, under conditions the manufacturer chose. Typically that means the item fixed or standing exactly as instructed, on a level surface or a sound wall, with the weight spread evenly and sitting still. It does not describe your garage, your wall, your fixings, or the way you will actually load it. It is a starting point, not a promise.

The rating also says nothing about how it was arrived at, unless the maker tells you. Some figures come from a test, some from a calculation, and some from a listing copied from another listing. On this site every capacity figure is attributed to the manufacturer or supplier that stated it, and where a supplier publishes no figure the product page says so rather than inventing one. Treat any rating without a source the same way.

None of this makes ratings useless. A shelf rated to carry a given weight is telling you something real about the steel and the design. It just is not telling you the thing you most want to know, which is what your wall will hold, and it is not telling you what happens when the load is not sitting still.

Per shelf and total are different numbers

A freestanding shelving unit usually carries two ratings: one per shelf and one for the whole unit. People assume the total is the per-shelf figure multiplied by the number of shelves. Often it is not, and it is lower, because the uprights and feet carry the sum of every shelf and they have a limit of their own. A unit rated generously per shelf can still be overloaded if every shelf is filled to that figure.

On the five-tier boltless shelving unit, the manufacturer's stated figures are 175kg per shelf and 875kg across the unit, which is five shelves at the shelf figure. Even where the numbers add up like that, the conditions still apply: the weight spread evenly across each shelf, not piled at the centre of a span, and the unit standing on a level floor. A garage slab with a drainage fall is not level, and a unit standing out of true carries less than its rating suggests.

Where a wall-mounted rack gives one figure for the whole rack, the same thinking applies in reverse: it is the total, and it assumes the load spread across every tier and every fixing. A rack loaded on its top tier only, with the lower ones empty, puts the whole weight where the leverage on the top fixings is greatest, and behaves worse than the same weight spread through the tiers.

A hook is harder than a shelf

The same weight is not the same load. A toolbox sitting on a shelf pushes straight down onto the shelf, and the shelf pushes down onto the uprights or the brackets. A toolbox hanging on a hook also pushes down, but the hook sticks out from the wall, so the weight tries to rotate the hook off the wall. The further the load sits from the wall, the harder that rotation pulls. Engineers call it a moment; the rest of us call it leverage.

That leverage lands on the fixings unevenly. The top fixing of a hook or bracket is pulled outwards, straight out of the wall, which is the direction a plug or anchor is weakest in. The bottom fixing is pushed into the wall. So a bracket with two screws is not sharing the load equally: the top one is doing the hard work, in the hardest direction. This is why a bike on an arm, a hose reel on a long hook or a bench on brackets is a much stiffer test than a shelf carrying the same weight.

Still, moving and dropped

Ratings are for a load that is sitting still. A garage is full of loads that are not. A bike lifted onto a hook lands on it. A ladder swung off a bracket jerks it. A drill dropped into its cradle from a few inches arrives with more force than its own weight. None of these is a dramatic event, but each one briefly loads the fixing harder than the resting weight, and it is the fixing, not the hook, that loosens a fraction each time.

This is the mechanism behind the hook that was fine for a year and then was not. Nothing changed about the weight; the fixing was being worked a little on every lift and swing, in a material that had a little give in it, until it had enough give to let go. The answer is not a bigger hook. It is a fixing in sound material, deep enough that working it does nothing.

The wall sets the limit, and there is no number for it

Every load on a wall passes through a chain: the item, its bracket, the screw, the plug or anchor, and the wall. The rating covers the first link. The chain fails at the weakest one, and in a UK garage the weakest is usually the last two. Aerated block on standard plugs, plasterboard on hollow anchors, a thin precast panel: each of these gives way long before a decent steel hook would.

Nobody can honestly tell you the figure for your wall without seeing it, and this guide will not pretend to. What can be said is what to do about it: identify the wall, choose the fixing for the wall rather than for the item, use every fixing hole the item provides, and for anything heavy or cantilevered, spread the load on a batten or move it to a freestanding unit. The ten-pack of steel hooks does not carry a stated load figure at all, which is a fair reflection of the fact that the hook is rarely the limit.