Can you guestimate how much weight furniture can support?

September 12, 2009 10:39 AM

Is there a simple convention about how much weight a piece of furniture can support?

I'd like to purchase a bookcase/sidetable that might serve as a stand for a largish fish tank. With water inside, a 30 or 40 gallon tank might weigh 300-400 pounds. Could for example this support such a tank when placed long-side down? Data on the safe limits of load on furniture appears to be generally lacking, and all-in-one tanks with their own base look horribly ugly.

posted by drpynchon to home & garden (10 comments total)

Your question gave me a flashback to high school physics tests. Here's something that might help, but be sure you aren't buying one material passed off as something else before calculating. Obviously. Remember a veneer on top of a slightly softer core material might technically support the weight, but the veneer might have less tolerance and crack/dent before the core gives way (if that makes any sense).
posted by variella at 10:45 AM on September 12

Th amount of weight an object can support is dependent upon the material it is made from and the thickness of that material.

Sheet metal will support much less weight than metal that is an inch thick. Balsa wood supports less weight than mahogany of the same thickness.

Etc.
posted by dfriedman at 10:49 AM on September 12

If that case is made of particle board, don't put a fish tank on top.
1. It's weaker
2. It's not water tolerant at all.

It's definitely a physics question. I like variella's link.
posted by SLC Mom at 11:01 AM on September 12

There is a lot more to take into consideration than simply the material and its thickness. A lightweight honeycomb panel can support a lot more weight than a panel made of plywood with similar thickness. Similarly, the structure itself needs to be able to withstand racking forces in addition to just the weight of the tank.
posted by kenliu at 11:05 AM on September 12

A properly designed structure made of cardboard would hold up that tank. So structural capacity is not really the issue. A flimsy piece of furniture like the one linked (assuming the likelihood that it's particleboard) would probably hold the tank up, too, and if the tank leaks, well, you've got other problems, but what I'd be concerned about is the rigidity of the base. Most of that particleboard furniture is pretty wobbly; i.e., the joints are not very strong. With 400 pounds on top of it, if somebody accidentally gives that tank a shove the whole piece might twist and fall. I'd recommend visiting a used furniture or antiques emporium and finding a nice old wash stand or commode. See for example the one at top left here, which you could purchase for $4 less than the thing you've linked to. Test anything for rigidity, but in my experience the old stuff was overbuilt and will last forever. I used to have a fishtank on just such a washstand. Supplies fit neatly underneath.
posted by beagle at 11:25 AM on September 12

The only thing that prevents this bookcase from shearing (going from rectangle to parallelogram) is (probably) a handful of dowels and a sheet of hardboard tacked to the back. Individual shelves in this unit are capable of supporting a given weight of books. But the unit as a whole is not designed to support a large excess weight on the top. As beagle says, particleboard furniture tends to be wobbly. The more off-balance it gets, the more the board rips and the looser everything gets.

My advice: if you want something that looks stylish and modern like that bookcase but will support 400lbs, have something made. It's a simple structure that could be put together relatively easily using heavy plywood or pine and the right fixings.
posted by le morte de bea arthur at 12:09 PM on September 12

Is there a simple convention about how much weight a piece of furniture can support?

No.

Almost any wood-based material could support that much weight easily, but everything depends on the structural design of the piece. Ideally there should be vertical pieces almost directly under the sides of the tank, carrying the load all the way down to the floor; you don't want a 4-foot tank in the middle of a table whose legs are 7' apart unless the tabletop itself is very strong, i.e. thick solid wood with a supporting skirt; not particleboard. Also, the corner joints on cheap casework like that shelving unit are quite weak, so it's only the back panel that keeps the whole think from parallelogramming to one side or the other and bucking under heavy loads. As mentioned above, if the back panel isn't very securely fastened then the whole structure is suspect.
posted by jon1270 at 12:52 PM on September 12

I should probably clarify that my link was intended to give an idea as to the kinds of stressors that need to be considered in addition to the material used.

I concur with all the answers given after mine- go for making something yourself for sure, but remember pine is hard to stain evenly; if you're looking at buying solid wood, I've done OK using solid birch (not plywood). Durable hardwood that stains easily, relatively inexpensive. I know there are some experienced woodworkers here that could give you good advice.
posted by variella at 1:10 PM on September 12

I've found that Ikea furniture especially things intended to be tv stands have max loads listed. However, with the advent of Plasma and LCD, televisions are a lot lighter than they used to be. Even something sturdy like this is only rated for 100kg.
posted by mmascolino at 1:12 PM on September 12

just in case you're in an apartment or the second floor of a home: make sure, not only that your furniture can support the load, but that your FLOOR can support the load as well. For example, 300-400 lbs over an area of 5 SF is safe (for a bookcase with a large contact area with the floor) but the same tank on a table with four legs (contact area appx. 0.25 SF)? You'll punch holes through your floor.

This is a structural engineering question, and if you don't feel comfortable figuring the answer out yourself, there are professionals who could do the calculation for you pretty quickly.
posted by Chris4d at 9:01 AM on September 14