Aquarium stand: span, deflection, panel thickness
A stand carries weight, not an aquarium, and it works as a beam. Getting the span 200 mm wrong costs more than a millimetre of plywood.
How the load travels down
The weight, margin included, spreads over the uprights. An overlay top takes it across its full area and passes it to the vertical panels. The further apart the uprights sit, the more the top sags between them.
What matters is not only whether the stand holds, but how far it bends. An aquarium does not tolerate tilt. Even a small sag in the top means the bottom pane no longer rests evenly: stress concentrates along one edge, and an edge is where a crack starts.
Why span goes to the fourth power
Deflection of a beam grows with the fourth power of the span. Double the span and deflection rises about 16 times. This is the single most important relationship in stand design, and it is the one most often ignored when a stand is copied from a photo.
The practical conclusion: a middle upright is almost always cheaper than moving to a thicker board. Halving the span is the same as making the material 16 times stiffer, and it costs one extra panel.
16 or 18 mm
Bending stiffness depends on thickness cubed. Going from 16 to 18 mm at the same span cuts deflection by roughly 1.4 times. For tanks from a metre up that is usually justified; for small ones it is money spent for nothing.
Material matters too. Plywood is stiffer than chipboard at the same thickness but dislikes moisture at the cut edge. MDF sits somewhere between the two, so the choice is rarely about price alone.
Cutting list and edge banding
A standard sheet is 2440 × 1220 mm, and the calculator knows other formats as well. The cutting plan shows how many parts come out of one sheet and how many sheets you have to buy, which is also your cost estimate.
Edge banding keeps moisture out of the chipboard core. Plywood does not need it: its edges are sanded and painted instead.
What the calculation leaves out
- humidity and the swelling of chipboard over the years;
- the quality of the fasteners and hardware;
- an uneven floor and a slope;
- diagonal stiffness, since the back panel often acts as a brace;
- the weight of equipment stored inside the stand.
Each of these can spoil a stand that passes on paper. The last one catches people who keep a canister filter and a CO₂ cylinder in the same cabinet and never count them.
In practice
- Put uprights under the corners and under the ribs of the tank, not where they look good.
- A back panel made from a full sheet adds more stiffness than it seems to.
- Adjustable feet rescue a stand on an uneven floor.
- Keep the stand off underfloor heating and out of direct sun.
The tank is the easy part to get right. The cabinet is where a 200 mm error in span costs more than an extra millimetre of plywood, which is why the numbers are worth running before the sheet is cut.
Calculator
The calculator takes your dimensions and works out glass, weight, stand and doses.
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