Aquarium Glass Thickness & Volume Calculator

How this calculator sizes your glass

The single most important number for aquarium safety is not the volume — it is the height of the water. Water pressure grows with depth, so a 60 cm tall tank pushes on its lower seams more than twice as hard as a 30 cm tank of the same total capacity. That is why two tanks holding the same litres can need very different glass. This tool treats each panel as an engineered plate and sizes it from the water height, the panel's proportions, the material and your chosen safety margin, rather than from a crude "divide the height by eighteen" rule of thumb.

The Warren plate-bending formula

Each vertical panel behaves as a rectangular plate carrying a triangular load — zero pressure at the surface, maximum at the base. The minimum safe thickness is:

t = √( β × H³ × 10⁻⁵ ÷ B )

Here t is the thickness in millimetres, H is the water height in millimetres, β (beta) is a coefficient set by the panel's shape, and B is the allowable bending stress — the material's tensile strength divided by your safety factor. For standard float glass a conservative tensile strength of 19.2 N/mm² is used, so at the industry-standard safety factor of 3.8 the allowable stress works out at about 5.05 N/mm².

Alpha and beta coefficients

A longer panel flexes far more than a short one of the same height, so the maths uses two coefficients read from the panel's proportions: beta for stress and required thickness, and alpha for how far the centre bows. For the vertical panels the ratio is length ÷ height; for the base it is length ÷ width. If your tank lands between two rows, the calculator interpolates the exact value.

Length ÷ Height	Alpha (bowing)	Beta (stress)
≤ 0.5	0.0030	0.0850
0.666	0.0085	0.1156
1.0	0.0220	0.1600
1.5	0.0420	0.2600
2.0	0.0560	0.3200
2.5	0.0630	0.3500
≥ 3.0	0.0670	0.3700

The base panel carries a uniform full-depth load instead of a triangular one, so it uses its own set of coefficients based on the length-to-width ratio:

Length ÷ Width	Alpha	Beta
1.0	0.0770	0.4530
1.5	0.0906	0.5172
2.0	0.1017	0.5688
2.5	0.1110	0.6102
≥ 3.0	0.1335	0.7134

Bowing, deflection and the DIN 32622 limit

Even glass thick enough never to break can still flex too much. Steady bowing tires the silicone seams and eventually leaks. The centre deflection is estimated as:

d = α × p × 10⁻⁶ × H⁴ ÷ ( E × t³ )

where p is the water pressure and E is the material's stiffness (about 69,000 N/mm² for glass, but only 3,300 for acrylic — which is why acrylic bows so much more). Bowing under one millimetre is invisible and fine; beyond three millimetres it is visibly distorting and risky. The German aquarium standard DIN 32622 draws the line at one five-hundredth of the panel's length, and the safety matrix above flags any thickness that crosses it.

Materials: glass, low-iron, tempered and acrylic

Standard float (annealed) glass is the default for home tanks — strong, cheap and it cracks slowly rather than shattering. Low-iron glass (Optiwhite, Starphire, Diamant) is mechanically identical but removes the green tint, so it is sized exactly the same and chosen purely for clarity. Tempered glass is much stronger and can be thinner, but it shatters all at once if deeply scratched or thermally shocked and cannot be drilled after treatment, so it is mostly a base material for big commercial tanks. Cast acrylic is far lighter but much more flexible, so a panel must be roughly 1.5 to 2 times thicker than glass to bow the same amount — yet the finished tank still ends up nearly half the weight.

How bracing lets you use thinner glass

An open, rimless top leaves the upper edge of each panel unsupported, which is the worst case. Tying the panels together at the top shortens the effective span and allows thinner glass. A trimmed plastic rim gives partial support and trims roughly 16% off the required thickness; a centre brace across the long panels roughly halves their span for around a 25–35% reduction; and a full euro-brace — a glass band bonded around the whole top rim — is the strongest, cutting the requirement by up to about 56%. Select your bracing and watch the recommendation move.

Reading the glazier cut list

A glass shop cuts each panel separately, so ordering the outside dimensions of the finished tank gives pieces that will not fit. Every joint has to lose the glass thickness plus the silicone gap. In the most common build — front and back running the full length, sides tucked between them, over a base that sits inside all four walls — the front and back are cut to the full outside length and height, each side is the outside width minus two glass thicknesses and two silicone gaps, and the base loses the same amount on both dimensions. The calculator does this subtraction for your exact build and layout, and the print button produces a clean sheet for the shop. A silicone gap of about 2–3 mm per metre of joint is typical: 1 mm for nano tanks, 1.5 mm for standard sizes, and 2.5–3 mm once the glass passes 15 mm.

Gross volume, net volume and weight

The gross figure is the full internal box; the net figure is what actually holds water once you allow for headspace at the top and the space taken by substrate, rocks and equipment — usually 80–90% of the label, which is why a "55-gallon" tank never really holds 55 gallons. The net volume is the number that matters for dosing and stocking. Weight adds up fast: water alone is about a kilogram per litre, and once you include the glass, a large tank can approach half a tonne when filled — enough that it should sit against a load-bearing wall or across the floor joists.

This tool gives careful engineering estimates to help you plan and talk to a fabricator with confidence. For a large, unusual or public installation, have the final design signed off by a qualified structural engineer or glazier before you build.