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Tank Dimensions

Length (mm) Front panel width

Width (Depth) (mm)

Height (mm)

Water Level (mm) Leave empty for full height

Configuration

Water Type

Glass Type

Bracing

Safety Factor

3.8

Industry standard: 3.8. Public aquariums: 5.0+

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About

Incorrect glass thickness selection is the primary cause of catastrophic aquarium failure. A 500-liter tank exerts over 490 Pa of hydrostatic pressure at the base of a 500 mm water column. The pressure distribution is triangular: zero at the surface, maximum at the substrate. This calculator derives minimum glass thickness t from panel span L, water depth h, fluid density ρ, and a configurable safety factor SF using rectangular plate bending theory. It accounts for glass type (float, tempered, laminated), bracing configuration, and water salinity. Results assume panels bonded with silicone at all edges. The formula approximates fixed-edge boundary conditions and does not account for seismic loads or thermal cycling.

Pro Tip: Tempered glass is stronger under uniform load but shatters entirely on point impact. For tanks above 1000 mm in any dimension, laminated glass is the professional standard. Always round up to the next commercially available thickness. Remember that bottom panels must support the full water column plus substrate weight, so they require separate consideration. This tool calculates the front/side panel thickness, which is the most critical failure point.

Formulas

The minimum glass thickness is derived from rectangular plate bending theory under triangular hydrostatic load. The maximum bending stress occurs at the base of the longest unsupported panel edge.

t = L × √SF × ρ × g × hσ × β

Where t = minimum glass thickness m, L = longest unsupported panel span m, SF = safety factor (typically 3.8), ρ = water density (1000 kg/m³ freshwater, 1025 kg/m³ saltwater), g = gravitational acceleration 9.81 m/s², h = water depth m, σ = allowable stress of glass (6.89 MPa for annealed float glass), β = support coefficient derived from the aspect ratio α = L ÷ H.

The support coefficient β is interpolated from plate theory tables. For a panel with all four edges fixed:

{

β ≈ 0.2874 if α ≤ 0.5β ≈ 0.3762 if α = 0.667β ≈ 0.7134 if α = 1.0β ≈ 1.0 if α ≥ 3.0

Hydrostatic pressure at depth h:

P = ρ × g × h

For braced tanks, the effective unsupported span L is reduced to the distance between the brace and the nearest edge, and the calculation is repeated for the reduced panel.

Reference Data

Tank Description	L mm	W mm	H mm	Volume L	Min Glass mm	Recommended mm
Nano Cube	300	300	300	27	4	5
10 Gallon Standard	510	260	350	38	5	6
20 Gallon Long	760	310	410	76	6	8
40 Gallon Breeder	910	460	410	151	8	10
55 Gallon Standard	1220	330	510	208	10	10
75 Gallon	1220	460	530	284	10	12
90 Gallon	1220	460	640	340	12	12
120 Gallon	1520	460	640	454	12	15
180 Gallon	1830	460	640	681	15	15
240 Gallon	2440	460	640	908	15	19
300 Gallon	2440	610	640	1136	19	19
Large Custom	3000	600	750	1350	19	22
XL Display	3660	610	760	1703	22	25

Frequently Asked Questions

Saltwater has a density of approximately 1025 kg/m³ compared to freshwater at 1000 kg/m³. This 2.5% increase in density produces a proportionally higher hydrostatic pressure at any given depth. For a 600 mm water column, the base pressure rises from 5886 Pa to 6032 Pa. In practice, this rarely changes the commercial glass size selected, but it can push a borderline calculation into the next thickness bracket.

A safety factor of 3.8 is the widely accepted industry standard for aquarium glass engineering, originally derived from German TÜV recommendations. It accounts for manufacturing defects in glass, micro-scratches from cleaning, thermal stress from heaters and lighting, and long-term static fatigue of glass under constant load. Reducing below 3.0 is not recommended for any permanent installation. Values of 4.0 to 5.0 are used for public aquariums or tanks with acrylic panels.

Yes. Euro-bracing (a strip of glass bonded around the top perimeter inside the tank) effectively reduces the unsupported vertical span of each panel. A 50 mm euro-brace on a 600 mm tall panel reduces the free span to approximately 550 mm. More critically, it constrains the top edge against outward deflection, converting the panel from a three-sided support condition to a four-sided support condition. This changes the support coefficient β significantly and can reduce required thickness by 1 - 3 mm depending on tank dimensions.

The bottom panel experiences uniform pressure equal to the full water column height plus the weight of substrate (gravel, sand, rock). For tanks under 500 mm in height, using the same thickness as the sides is generally acceptable because the bottom panel is fully supported by the stand. For taller tanks, the bottom panel should be 1 - 2 mm thicker than the sides, or a foam mat should be placed between the glass and the stand to distribute point loads and prevent stress fractures.

Tempered glass is approximately 4 - 5 times stronger than annealed float glass under uniform load. However, it fails catastrophically: the entire panel disintegrates into small fragments instantly. It cannot be drilled or cut after tempering. Laminated glass consists of two annealed sheets bonded with a PVB or EVA interlayer. Its strength is slightly lower than tempered, but on failure, the interlayer holds fragments in place, preventing total water loss. For tanks above 300 liters, laminated glass is preferred for insurance and safety reasons.

Glass exhibits static fatigue: under constant load, micro-cracks propagate slowly. Elevated temperatures accelerate this process. Aquarium heaters creating localized hot spots near 30 - 35 °C on the glass surface can reduce effective long-term strength by 10 - 15% over years. The safety factor of 3.8 partially accounts for this. Place heaters away from glass walls and ensure adequate water circulation to minimize thermal gradients across the panel.

No. Acrylic has fundamentally different mechanical properties. Its modulus of elasticity is approximately 3.2 GPa compared to glass at 70 GPa. Acrylic deflects significantly more under load but has higher impact resistance. The allowable stress, creep behavior, and bonding method (solvent welding vs. silicone) require entirely different calculations. Using glass formulas for acrylic would produce dangerously thin results.