Glass · Structural
Aquarium glass thickness calculator: rimless and braced
A rimless aquarium needs thicker glass than most hobby charts say. Those charts take the top edge of the front as held, which only a frame or a top brace that works can do. With the top edge free, the stress in a front two to two and a half times as long as it is high is 44 to 58 % higher than those charts say. This calculator works out each pane with the water to the brim, for the top edge you really have, on the thinnest the glass can be delivered, and shows every step.
Show the working
Show the working
Show the working
Show the working
Show the working
Everything is computed in your browser — no upload, no sign-up, nothing about your tank leaves your machine. Every coefficient and every formula used is written out below, so you can check the result instead of trusting it.
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Aquarium glass thickness chart
The thinnest stock glass for common tank sizes, annealed float with polished edges and fresh water to the brim, in mm. These are the calculator's own figures, produced by the same code. The braced columns assume a glass top brace that holds the edge; the calculator checks yours from its sizes. “> 19” means more than 19 mm: no thickness, an engineer's job.
| Tank, cm | Litres | Rimless: front and back | Rimless: ends | Braced: front and back | Braced: ends | Bottom on its edges only |
|---|---|---|---|---|---|---|
| 45 × 30 × 30 | 41 | 5 | 4 | 4 | 4 | 6 |
| 60 × 30 × 36 | 65 | 6 | 4 | 6 | 4 | 8 |
| 60 × 45 × 45 | 122 | 8 | 6 | 8 | 6 | 10 |
| 80 × 35 × 40 | 112 | 8 | 5 | 8 | 5 | 10 |
| 90 × 45 × 45 | 182 | 10 | 6 | 8 | 6 | 12 |
| 100 × 40 × 50 | 200 | 12 | 8 | 10 | 6 | 12 |
| 120 × 50 × 50 | 300 | 12 | 8 | 10 | 8 | 15 |
| 120 × 60 × 60 | 432 | 15 | 10 | 12 | 10 | 19 |
| 150 × 50 × 60 | 450 | 19 | 10 | 15 | 8 | 15 |
| 150 × 60 × 60 | 540 | 19 | 10 | 15 | 10 | 19 |
| 180 × 60 × 60 | 648 | 19 | 10 | 15 | 10 | 19 |
| 200 × 60 × 70 | 840 | > 19 | 12 | 19 | 10 | > 19 |
A bottom resting on its full surface takes the thickest wall. Laminated or toughened glass, sea water, edges that are not polished, a pond window or a size that is not here: type it in above.
How this is calculated
Each wall is a plate on its four edges. The two vertical edges and the bottom one are held by the neighbouring panes, simply supported: silicone does not clamp them. The top edge is free in a rimless tank, or held by a glass top brace. The water pushes from nothing at the top to q at the bottom. Small-deflection plate theory (Kirchhoff), solved for that load with Lévy's series:
β and α depend on r = length of the pane / H and on the top edge. They are interpolated in this table, worked out for ν = 0.23. An r under 0.5 takes the 0.5 row, which is on the safe side; cR is the reaction on a top edge that is held, used to check the brace.
| r = L/H | Free top: β | Free top: α | Held top: β | Held top: α | Held top: cR |
|---|---|---|---|---|---|
| 0.50 | 0.0840 | 0.00397 | 0.0824 | 0.00387 | 0.0524 |
| 0.75 | 0.1388 | 0.01464 | 0.1212 | 0.01221 | 0.0968 |
| 1.00 | 0.1977 | 0.03996 | 0.1548 | 0.02335 | 0.1301 |
| 1.25 | 0.2781 | 0.09000 | 0.2078 | 0.03448 | 0.1505 |
| 1.50 | 0.3516 | 0.16501 | 0.2522 | 0.04409 | 0.1618 |
| 1.75 | 0.4120 | 0.26529 | 0.2871 | 0.05180 | 0.1675 |
| 2.00 | 0.4599 | 0.39018 | 0.3137 | 0.05772 | 0.1700 |
| 2.25 | 0.4971 | 0.53875 | 0.3333 | 0.06218 | 0.1708 |
| 2.50 | 0.5535 | 0.71007 | 0.3478 | 0.06548 | 0.1707 |
| 2.75 | 0.6164 | 0.90334 | 0.3583 | 0.06790 | 0.1702 |
| 3.00 | 0.6791 | 1.11792 | 0.3659 | 0.06966 | 0.1696 |
| 3.50 | 0.8043 | 1.60912 | 0.3753 | 0.07185 | 0.1690 |
| 4.00 | 0.9294 | 2.18090 | 0.3801 | 0.07298 | 0.1688 |
| 5.00 | 1.1795 | 3.56047 | 0.3837 | 0.07384 | 0.1687 |
The chart most aquarium sites copy is the held-top half of this table. Its coefficients, 0.085 to 0.37 for r = 0.5 to 3, are the classical ones for a plate held on all four edges, and this calculation gives them again within 1 to 2 %. On a rimless tank the top edge is free and the stress is higher than that chart says: 9 % at r = 0.75, 24 % at r = 1, 44 % at r = 2 and 58 % at r = 2.5. From r = 2.5 the largest stress is no longer at the middle of the top edge but near the ends, where the pane twists, and that is the one used. Past r = 3 a free top edge is not calculated: it needs a brace.
Strength and safety factor
Glass is weaker under a load that never goes away, and water never goes away. The design strength follows the form of EN 16612 for a permanent load. EN 16612 is written for glazing in buildings and does not cover aquariums: this is its method and its coefficients, not a claim of compliance.
That allows σadm = 5.37 N/mm² on annealed float with polished edges, 4.30 N/mm² on a free edge that is not polished, and 51.7 N/mm² on toughened glass. The hobby's “19.2 / 3.8 = 5.05 N/mm²” is close: what separates the two methods is the top edge, not the allowable stress. ke applies only where a free edge is in tension: the top of a rimless wall and the inner edge of a brace.
Thickness, tolerance and deflection
Glass can be delivered a little thinner than its nominal thickness (EN 572-2). With a flood at stake the calculator checks the minimum, not the nominal, and takes the thinnest stock thickness whose minimum passes. It also keeps the deflection under half that minimum, the range where small-deflection theory holds; on annealed glass sized for stress that never decides, on toughened glass it often does.
| Nominal, mm | 4 | 5 | 6 | 8 | 10 | 12 | 15 | 19 |
|---|---|---|---|---|---|---|---|---|
| Tolerance, mm | ±0.2 | ±0.2 | ±0.2 | ±0.3 | ±0.3 | ±0.3 | ±0.5 | ±1.0 |
| Minimum, mm | 3.8 | 4.8 | 5.8 | 7.7 | 9.7 | 11.7 | 14.5 | 18.0 |
Laminated and toughened glass
- Laminated float, two equal plies with PVB. Under a permanent load PVB transfers almost no shear, so each ply is taken as working alone: tef,σ = √2 · t, tef,w = ∛2 · t, and the deflection is kept under half a ply. If one ply breaks the other still holds the water. Recommended above about 1000 litres.
- Toughened (tempered): about ten times the design strength of annealed glass under a permanent load, so the deflection, not the stress, usually decides its thickness. When it breaks it falls apart and the tank empties at once, and it can break by itself from a nickel sulphide inclusion. A single toughened pane is given only up to 100 litres; above that the page asks for laminated glass.
- Laminated toughened: two toughened plies with PVB, calculated as laminated. Ask for heat-soaked glass (EN 14179) and have every hole made before toughening.
Top brace and bottom
A glass top brace (euro brace) is a strip glued flat inside the top edge. It works as a beam in its own plane, between the corners or the cross braces, loaded by the wall's top reaction R = cR · q · H. It is checked as annealed float on its minimum thickness: the stress at its inner, free edge, and its stiffness — it may bend at most a tenth of what the top of the wall would move with no brace. A brace that fails either check does not hold the edge, and the wall is calculated as rimless. The plastic rim of a mass-produced tank is not taken as a brace.
A bottom on its full surface, on a mat over a flat, level top, passes the water straight into the stand: there is no bending to calculate, and by common practice it takes the thickest wall. A bottom on its edges only, on an open frame, is a plate on four edges under the water and its own weight (2500 kg/m³), from this table (ν = 0.23), with b the short side:
| Long side / short side | β | α |
|---|---|---|
| 1.00 | 0.2718 | 0.04617 |
| 1.25 | 0.3825 | 0.06850 |
| 1.50 | 0.4752 | 0.08779 |
| 1.75 | 0.5478 | 0.10323 |
| 2.00 | 0.6028 | 0.11511 |
| 2.50 | 0.6735 | 0.13065 |
| 3.00 | 0.7109 | 0.13903 |
| 4.00 | 0.7401 | 0.14569 |
| 5.00 | 0.7476 | 0.14742 |
A window in a pond or pool wall
A window held on its four edges in a frame, its top d under the water surface, carries a uniform ρ·g·d plus a triangle from 0 to ρ·g·h over its height h. The largest stress of each part (the bottom table, and the held-top half of the first one) are added, which is on the safe side. Laminated glass only, and the limits below apply: a pool window is not sized here.
Checked against real tanks
The best-known rimless tanks, the ADA Cube Garden 60-P, 90-P and 120-P, with the front thickness their retailers list: the calculator gives the maker's thickness for all three, the hobby chart is a step short on the two larger ones.
| Tank, cm | Maker | This calculator | Hobby chart |
|---|---|---|---|
| 60 × 30 × 36 | 6 | 6 | 6 |
| 90 × 45 × 45 | 10 | 10 | 8 |
| 120 × 50 × 50 | 12 | 12 | 10 |
Worked example you can check by hand
The tank this page opens with: 120 × 50 × 50 cm, rimless, annealed float with polished edges, fresh water. The front: r = 1200 / 500 = 2.4, between the 2.25 and 2.5 rows, β = 0.5309 and α = 0.6415.
10 mm would not do: its minimum, 9.7 mm, is under 11.01. Type the tank into the calculator above and you should get exactly these figures. If you ever find the calculator disagrees with this example, the calculator is wrong and we want to know.
What this page does not do
- No joints. The silicone is not calculated: not its width, its thickness or its make. Use a silicone made for aquariums.
- No holes, cut-outs or overflows in the glass; no curved, corner, bow-front or acrylic tanks, no sloping panes, no tank built into furniture.
- No stand and no floor. You get the total weight; whether the stand and the floor carry it is another check.
- A flat, level base. A bottom on its full surface needs one; how flat depends on the stand and is not given here.
- Sound glass. A deep scratch or a chipped edge lowers the strength: none of this applies to damaged glass.
- No public aquarium, pool or large pond. Over 19 mm of glass, 80 cm of height, 1500 litres or 250 cm of length the page gives no thickness: that is an engineer's job. For laminated glass the 19 mm is its effective thickness, √2 times a ply.
Questions people ask
- How thick should aquarium glass be?
- It depends on the height of the water more than on anything else, then on the length of each pane and on whether its top edge is free or held by a brace. With the water to the brim, annealed float and polished edges, a rimless 120 × 50 × 50 cm tank needs 12 mm for the front and back and 8 mm for the ends; a 60 × 30 × 36 cm one needs 6 mm and 4 mm.
- Why does a rimless aquarium need thicker glass?
- Because the top edge of each pane is free. The chart most aquarium sites copy is the one for a plate held on all four edges, which is only true with a frame or a top brace that holds. With the top edge free the stress is 24 % higher than that chart says in a pane as long as it is high, and 44 to 58 % higher in a front two to two and a half times as long as it is high.
- Can an aquarium be made of toughened glass?
- A small one can, but toughened glass falls apart all at once when it breaks and the tank empties in seconds, and it can break by itself from a nickel sulphide inclusion. This calculator gives a single toughened pane only up to 100 litres; above that it asks for laminated glass, laminated float or laminated toughened.
- What safety factor is used for aquarium glass?
- The hobby uses 19.2 N/mm² divided by a factor of 3.8, which allows 5.05 N/mm². This calculator uses the form of EN 16612 for a permanent load instead: 0.29 × 45 / 1.8 = 7.25 N/mm², divided by 1.35 for the water load, which allows 5.37 N/mm² on annealed float with polished edges. The two are close; the difference that matters is the free top edge.