Aquarium glass thickness calculator
Planning a DIY or custom tank? Enter the size to estimate how thick the front, end and bottom glass should be — then have a glass supplier or engineer check it.
This is an estimate, not a design. Glass fails suddenly and a full tank holds hundreds of pounds of water. Before you cut or order glass, confirm the thickness with the tank manufacturer, your glass supplier or a structural engineer, especially for tanks over about 24 inches tall, anything with holes drilled near an edge, or tanks in public spaces.
The formula
Each wall is treated as a flat plate held along the bottom and both sides by the silicone seams, with the top edge free (a rimless tank with no braces), loaded by water pressure that grows from zero at the surface to ρ × g × H at the bottom. The bending stress in such a plate is σ = β × ρg × H³ ÷ t², so the thickness that keeps it under the allowable stress is:
t = √( β × ρg × H³ × SF ÷ σ )
- t — glass thickness (mm). H — water depth (mm); the calculator assumes the tank is filled to the top.
- ρg — weight of fresh water, 1,000 kg/m³ × 9.81 m/s² = 0.00000981 N/mm³.
- σ — 19.3 N/mm² (MPa), the bending strength for annealed float glass used by the common hobby calculators. Some versions round it to 19.2.
- SF — safety factor, 3.8 by default, so the glass works at about 5.1 N/mm². Many builders use 4–5 for large or show tanks.
- β — a plate coefficient that depends on the panel's shape: length ÷ height for the front, back and ends; long side ÷ short side for the bottom. Values between the rows below are interpolated; ratios under 0.5 or over 3 use the end rows.
| Ratio | β, walls (L ÷ H) | β, bottom (long ÷ short) |
|---|---|---|
| 0.5 | 0.085 | — |
| 0.666 | 0.1156 | — |
| 1 | 0.16 | 0.453 |
| 1.5 | 0.26 | 0.5172 |
| 2 | 0.32 | 0.5688 |
| 2.5 | 0.35 | 0.6102 |
| 3 | 0.37 | 0.7134 |
Worked example
A rimless 24 × 10 × 16 inch tank (610 × 254 × 406 mm), filled to the top. Front panel: L ÷ H = 1.5, so β = 0.26 and t = √(0.26 × 0.00000981 × 406.4³ × 3.8 ÷ 19.3) = 5.8 mm (0.23 in) — buy 6 mm. End panels (ratio 0.63, β 0.108): 3.7 mm. Bottom (ratio 2.4, β 0.602): 8.8 mm (0.35 in) — buy 10 mm. Published hobby calculators using the same method give 0.23 in and 0.35 in for this tank.
Thickness by tank height
For a typical front panel twice as long as it is tall (β = 0.32), the minimum thickness depends only on the water depth and the safety factor:
| Water depth | SF 3.8 | SF 4.5 | SF 5.0 |
|---|---|---|---|
| 12 in (30.5 cm) | 4.2 mm → 5 mm | 4.6 mm → 5 mm | 4.8 mm → 5 mm |
| 16 in (40.6 cm) | 6.4 mm → 8 mm | 7.0 mm → 8 mm | 7.4 mm → 8 mm |
| 18 in (45.7 cm) | 7.7 mm → 8 mm | 8.4 mm → 10 mm | 8.8 mm → 10 mm |
| 20 in (50.8 cm) | 9.0 mm → 10 mm | 9.8 mm → 10 mm | 10.3 mm → 12 mm |
| 21 in (53.3 cm) | 9.7 mm → 10 mm | 10.5 mm → 12 mm | 11.1 mm → 12 mm |
| 24 in (61.0 cm) | 11.8 mm → 12 mm | 12.9 mm → 15 mm | 13.6 mm → 15 mm |
| 28 in (71.1 cm) | 14.9 mm → 15 mm | 16.2 mm → 19 mm | 17.1 mm → 19 mm |
| 30 in (76.2 cm) | 16.5 mm → 19 mm | 18.0 mm → 19 mm | 19.0 mm → 19 mm |
Thickness grows with the height to the power 1.5: doubling the height needs about 2.8 times the glass. Length matters much less, which is why a 72-inch tank and a 48-inch tank of the same height use similar glass.
Standard tanks compared
The formula is for unbraced rimless glass. Mass-produced framed tanks are thinner because the plastic rim and center brace hold the top edge, and their makers test them for their own designs. Do not use this table to judge whether your tank is safe; it shows why a DIY rimless copy of a standard size needs thicker glass than the original.
| Tank (outside) | Front, rimless SF 3.8 | Bottom | Typical framed tank |
|---|---|---|---|
| 5 gallon 16 × 8 × 10 in | 2.9 mm (0.12 in) | 4.2 mm (0.17 in) | 1/8 in (3 mm) |
| 10 gallon 20 × 10 × 12 in | 3.9 mm (0.15 in) | 5.6 mm (0.22 in) | 1/8 in (3 mm) |
| 15 gallon 24 × 12 × 12 in | 4.2 mm (0.16 in) | 5.6 mm (0.22 in) | 3/16 in (5 mm) |
| 20 gallon high 24 × 12 × 16 in | 5.8 mm (0.23 in) | 8.6 mm (0.34 in) | 3/16 in (5 mm) |
| 20 gallon long 30 × 12 × 12 in | 4.4 mm (0.17 in) | 5.8 mm (0.23 in) | 3/16 in (5 mm) |
| 29 gallon 30 × 12 × 18 in | 7.2 mm (0.28 in) | 10.6 mm (0.42 in) | 3/16 in (5 mm) |
| 40 gallon breeder 36 × 18 × 16 in | 6.6 mm (0.26 in) | 8.6 mm (0.34 in) | 1/4 in (6 mm) |
| 40 gallon long 48 × 12 × 16 in | 6.9 mm (0.27 in) | 9.6 mm (0.38 in) | 1/4 in (6 mm) |
| 55 gallon 48 × 13 × 21 in | 9.9 mm (0.39 in) | 14.5 mm (0.57 in) | 1/4 in (6 mm) |
| 65 gallon 36 × 18 × 24 in | 10.7 mm (0.42 in) | 15.8 mm (0.62 in) | 3/8 in (10 mm) |
| 75 gallon 48 × 18 × 21 in | 9.9 mm (0.39 in) | 13.7 mm (0.54 in) | 3/8 in (10 mm) |
| 90 gallon 48 × 18 × 24 in | 11.8 mm (0.47 in) | 16.8 mm (0.66 in) | 3/8 in (10 mm) |
| 125 gallon 72 × 18 × 21 in | 10.4 mm (0.41 in) | 14.5 mm (0.57 in) | 3/8 in (10 mm) |
| 150 gallon 72 × 18 × 28 in | 15.7 mm (0.62 in) | 22.3 mm (0.88 in) | 1/2 in (13 mm) |
What this does not cover
- Bracing: a euro brace or center brace changes the support conditions; this formula ignores it, so it errs thick for braced tanks.
- Tempered and laminated glass: tempered glass is stronger but cannot be cut or drilled after tempering; laminated glass behaves differently under load. Ask the supplier.
- Bottom support: the bottom value assumes the tank sits flat on a level stand, ideally on a foam or rubber mat. A bottom resting only on a frame or with point loads needs more.
- Acrylic: acrylic is far more flexible and needs its own formula — not this one.
- Holes and overflows: drilled holes weaken a panel, especially near edges; keep them well away from the seams.
Once the glass is sorted, estimate the finished weight with the weight calculator — the stand and floor carry all of it.
FAQ
How thick should glass be for a 55-gallon rimless tank?
For a 48 × 13 × 21 inch rimless tank filled to the top, the plate formula with a 3.8 safety factor gives about 10 mm for the front and back and about 15 mm for the bottom. Framed, braced 55-gallon tanks are commonly made with about 1/4-inch (6 mm) glass because the rim and center brace support the top edge — do not copy that thickness for a rimless build.
What safety factor should I use for aquarium glass?
3.8 is the usual hobby standard. Many builders use 4 to 5 for tall, large or public tanks. A higher factor means thicker, heavier and more expensive glass, but more margin for scratches, imperfect seams and an uneven stand.
Does the length of the tank affect glass thickness?
Less than height. The thickness depends on the water depth to the power 1.5 and on the length-to-height ratio only through the β coefficient, which levels off for panels more than about three times as long as they are tall.
Is this calculator enough to build a tank?
No. It is an estimate for planning and comparing options. Confirm the final thickness with your glass supplier, the tank manufacturer or a structural engineer before building.