🐟 Plywood Aquarium Calculator — Tank Glass & Acrylic Thickness

The build order: base, shell, seal, front

A plywood aquarium succeeds or fails on sequence. The calculator gives the four numbers below in one pass, but they land in a strict order on the bench — and each step has a threshold where the rules change:

1. 1Rigid, perfectly level base. Plywood tanks have no flex to spare — a twist of 1/8" across the base puts permanent shear into the epoxy seams before a drop of water goes in. Shims are part of the build, not an afterthought.
2. 2Plywood shell — the calculator’s sheet count. 3/4" panels with exterior or marine glue, bottom doubled on tanks past 300 gallons. Interior-grade glue is the one material decision that cannot be corrected after fill day.
3. 3Full epoxy coating — every surface that touches water. Two immersion-rated coats, ~60 sq ft per mixed gallon per coat, fiberglass cloth over seams on big shells. A pinhole the size of a pencil lead weeps a gallon a day at 22" of head pressure.
4. 4Front panel from the depth table. Glass or acrylic, chosen by water depth and panel width — never by what the lumber yard had in stock that week.

Front panel thickness vs water depth

Depth drives everything: pressure at the bottom of the panel is depth × 0.433 psi, and plate bending stress grows with the square of panel width on top of that. These values carry a 3.8 safety factor on edge-supported panels up to 48" wide — wider fronts need vertical stiffeners and engineering, not bigger numbers from this table:

Water weight quick reference

The number that ends most plywood-tank conversations is not volume — it is weight. Water runs 8.34 lb per US gallon, and the family of tank sizes below shows how fast the total escalates:

🐟Shell first, seal second, water last

Shell first, seal second, water lastPhoto: Unsplash

Why glass thickness does not double when depth doubles

The counter-intuitive scaling in the thickness table is the single most valuable thing to understand before sizing a tank. Water pressure grows linearly with depth — 12" of head is 4.3 psi at the bottom, 48" is 17.3 psi. If pressure alone ruled, glass would scale in straight steps. It does not, because plate bending stress also grows with the square of the unsupported span, and deeper tanks are effectively “wider” in the direction the panel bends:

• 1.12" → 24" depth (2×): glass goes 1/4" → 1/2", exactly 2× — pressure doubling dominates while the panel is small.
• 2.24" → 48" depth (2×): glass goes 1/2" → 1", still 2× on paper — but the stiffness margin is thinner, which is why the 48" row assumes ribbed or blocked edges and stops there.
• 3.Beyond 48" of head: no table row. Thickness alone stops paying: a 60"-deep front needs vertical stiffeners breaking the panel into ≤48" columns, and the safety-factor math belongs to a person who can see the whole build.

Floor load: the 300-gallon threshold

Siting beats reinforcement: a tank placed with its long axis perpendicular to the joists, near a bearing wall, engages many joists at their strongest point — the same principle as subfloor layout. The plywood span calculator shows how far a joist can carry the load, and the plywood weight calculator prices the shell’s share of the total before water ever enters the picture.

Plywood aquarium FAQs