Aquarium Glass Thickness Calculator
Enter your aquarium length, width, and water height to find the minimum glass thickness your tank requires. The calculator applies the standard AGA (American Glass Association) formula with a configurable safety factor, gives you separate results for the side/front panels and the bottom panel, flags the nearest commercial glass size to buy, and also shows total volume, glass weight, and water weight. Switch between metric and imperial units at any time.
Why glass thickness matters in aquarium design
An aquarium is a pressure vessel. Even a modest 120-litre tank exerts roughly 60 kg of hydrostatic force on the lower third of its side panels. Use glass that is too thin and the panel will bow, stress the silicone seams, and eventually crack - often without warning and always catastrophically. The AGA (American Glass Association) formula used in this calculator is the industry standard for DIY and commercial aquarium construction: it calculates the thickness a panel needs so the stress inside the glass stays well below the material's breaking point, multiplied by a safety factor to account for imperfections, temperature cycling, and the unpredictable way real glass fails.
How to read the results: minimum thickness vs. the commercial size to buy
The calculator gives you two numbers for each panel type. The "minimum thickness" is the theoretical lower bound: any glass thinner than this will eventually fail under the water load. The "buy this size" figure rounds up to the nearest standard commercial thickness - typically 4, 5, 6, 8, 10, 12, 15, or 19 mm - because glass is sold in fixed increments and you should always go up, never down. The side and front panels carry the same load (they see the same water column), so they share one calculation. The bottom panel bears a distributed load over its entire area rather than a pressure gradient, and its critical dimension is the shorter base edge, so it often comes out thinner than the side panels for wide, shallow tanks, and thicker for tall, narrow ones.
Safety factor, deflection, and choosing the right glass type
The default safety factor of 3.8 is the value specified by the AGA for aquariums and is widely used by professional tank builders. It means the glass can theoretically withstand 3.8 times the actual water load before reaching its rated stress limit. A higher value (4.0 to 5.0) adds extra margin for saltwater tanks (denser water, corrosive environment), tanks with strong circulation pumps that create dynamic pressure, or tanks deeper than 60 cm. The deflection output tells you how much the panel will bow at its centre under load: anything under 1 mm is imperceptible; 1-2 mm is safe but visible; above 2 mm you should consider the next thickness up. Float glass (standard window glass) works well for most tanks. Tempered glass is 4-5 times stronger, allowing thinner panels, but must be ordered pre-cut because it shatters if scored after tempering. Borosilicate glass (like Schott Duran) is used in laboratory tanks and very hot setups: it resists thermal shock but is expensive and rarely available in the large pane sizes big tanks need.
Silicone, cabinet support, and the total weight you need to plan for
Getting the glass right is only half the job. The panels are held together with structural aquarium-grade silicone, not ordinary bathroom sealant: the difference is the plasticiser content, which leaches into the water at concentrations harmful to fish. Apply a continuous bead with no air pockets, smooth it flat with a wet finger, and allow a full 24-48 hours cure at room temperature before adding any water. The water weight output shows why cabinet strength matters: a 300-litre tank weighs roughly 300 kg when full, plus glass (typically 20-40 kg) and substrate (another 20-60 kg for a planted tank). That is more than some floors can bear at a single point - check your floor rating or spread the load with a stand that distributes weight across multiple joists.
Standard glass thickness guide by tank size
| Tank size (cm) | Approx. volume | Side/front glass | Bottom glass |
|---|---|---|---|
| 30 x 20 x 20 | 12 L | 4 mm | 4 mm |
| 60 x 30 x 30 | 54 L | 5 mm | 5 mm |
| 90 x 40 x 40 | 144 L | 6 mm | 6 mm |
| 120 x 50 x 50 | 300 L | 8 mm | 6 mm |
| 150 x 60 x 60 | 540 L | 10 mm | 8 mm |
| 180 x 60 x 70 | 756 L | 12 mm | 10 mm |
| 200 x 80 x 80 | 1280 L | 15 mm | 12 mm |
| 240 x 90 x 90 | 1944 L | 19 mm | 15 mm |
Recommended commercial glass thicknesses for common aquarium sizes. Safety factor 3.8, float glass.
Frequently asked questions
What safety factor should I use for my aquarium?
The AGA recommends 3.8 as the standard minimum for aquariums. Use 3.8 for freshwater tanks up to 150 cm long and 60 cm deep. Use 4.0 to 4.5 for saltwater or reef tanks (salt water is slightly denser and the environment is more corrosive), tanks deeper than 60 cm, or tanks with powerful flow pumps. A higher safety factor means you end up with slightly thicker glass, which also reduces deflection and makes the seams last longer.
Do I need different thickness glass for the bottom panel?
Yes, but the direction of the difference depends on the tank shape. The bottom panel bears a uniform pressure load over its entire area, and its critical dimension is the shorter edge of the base. For wide, shallow tanks the bottom is often thinner than the sides; for tall, narrow tanks it can be thicker. This calculator works out both values separately, so always check both outputs and buy the correct pane for each.
Can I use tempered glass for my DIY aquarium?
Yes, and it is the preferred choice for large tanks. Tempered glass is 4-5 times stronger than float glass, meaning the required thickness is significantly smaller, which saves weight and cost at large sizes. The critical constraint is that tempered glass cannot be cut, drilled, or notched after tempering: it will shatter immediately. Order each panel pre-cut to your exact dimensions, including any bulkhead holes, before tempering. Never try to cut tempered glass yourself.
What happens if my glass is too thin?
Under-thickness glass will bow visibly at the centre of the panel. Over time this cyclic stress fatigues the silicone seams at the corners and edges, leading to slow leaks or sudden catastrophic failure. Glass does not give warning cracks before it breaks: when it goes, it goes all at once, releasing hundreds of litres of water and sharp shards onto your floor. Always use the next commercial size up from the calculated minimum, never round down.
Does the formula work for acrylic or polycarbonate tanks?
No. The formula in this calculator is derived from the elastic modulus and allowable stress of glass. Acrylic (PMMA) has a much lower modulus (about 3 GPa vs. 70 GPa for glass) and a different failure mode: it creeps slowly rather than breaking suddenly. Acrylic tanks need a separate calculation - typically a minimum thickness about 1.5 to 2 times greater than glass for the same panel dimensions, and they must be bonded with solvent cement, not silicone.
How do I calculate the total weight my cabinet needs to support?
Add water weight + glass weight + substrate weight + equipment weight. This calculator gives you the water and glass weights. Substrate adds roughly 1.5-2 kg per litre of substrate volume (a 5 cm deep substrate layer in a 120 x 50 cm tank is about 30 litres, so 45-60 kg). Filtration, rocks, and decor can add another 10-30 kg for a typical setup. A 300-litre planted tank commonly reaches 400-500 kg total: that is the weight of four to five adult people concentrated on a single stand footprint.