Aquarium acrylic thickness calculator

How this works

Each wall of a tank is treated as a flat plate held along its bottom and both sides, with the top edge free, loaded by water pressure that rises steadily from zero at the surface to its maximum at the bottom. The calculator works out two thicknesses and gives you the larger one.

Strength

t = √(β × q × H² ÷ σ), then × 1.5 for an open top

• H is the water height in inches.
• q is the water pressure at the bottom: 0.0361 psi per inch of fresh water (62.4 lb/ft³), so q = 0.0361 × H. Salt water is about 2.5% more.
• σ is the maximum permissible stress: 750 psi for cast acrylic in aquariums, the figure used in the CYRO (now Acrylite) aquarium sizing method. Acrylic's short-term tensile strength is about 10,000 psi, but under constant load for years it creeps and can craze, so long-term design stresses are kept far lower. Acrylite limits even general continuous loads to 750 to 1,500 psi.
• β is a plate coefficient that depends on the panel's length divided by its height: 0.120 at 0.5, 0.321 at 1.0, 0.523 at 1.5, 0.677 at 2.0, 0.866 at 3.0, and 0.940 at 4.0, interpolated in between.
• Open top: a panel with a free top edge bends more, so the method multiplies the thickness by 1.5. A bonded rim or cross braces holds the top edge and removes that factor.

Stiffness

Acrylic is strong but flexible, about 20 times less stiff than glass, so a panel thick enough not to break can still bow out noticeably. The bulge at the worst point is about w = α × γ × H⁵ ÷ (E × t³), with E = 450,000 psi and α another plate coefficient (0.003 at a ratio of 0.5, 0.022 at 1.0, 0.056 at 2.0, 0.067 at 3.0). We keep the bulge to no more than half the panel thickness. Past that, the panel is visibly bowed and the simple plate formula stops being reliable. For most real tanks, stiffness decides the thickness, not strength.

Worked example

A panel 48 in. long with 24 in. of fresh water. Length ÷ height = 2.0, so β = 0.677.

• Pressure at the bottom: q = 0.0361 × 24 = 0.866 psi.
• Braced top: t = √(0.677 × 0.866 × 24² ÷ 750) = √0.450 = 0.671 in.
• Open top: 0.671 × 1.5 = 1.007 in., the same answer Acrylite's aquarium calculator gives for this tank.
• Stiffness: t⁴ = 2 × 0.056 × 0.0361 × 24⁵ ÷ 450,000 = 0.0716, so t = 0.517 in. Strength governs here.

So a 48 × 24 in. panel needs about 3/4 in. cast acrylic with a braced top, and about 1 in. with an open top. That's thicker than many quick online calculators suggest, because it uses the long-term stress acrylic can carry for years, not its short-term breaking strength.

What this leaves out

The bottom panel, the seams, top bracing (a rim or cross braces changes the numbers a lot), stand support, temperature, and long-term creep. Joints are often the weakest point of an acrylic tank, and they depend on technique more than thickness. Read acrylic aquarium thickness for the full picture, and whether acrylic is safe for fish and reptiles.