Aquarium Glass Thickness Calculator
Enter your planned water height to get a safe starting glass thickness for a DIY aquarium build, plus a bracing recommendation based on tank length. Use this to plan, then confirm with a professional before you build.
The main driver: water pressure sets the thickness.
Used to flag whether bracing is recommended.
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recommended thickness
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imperial equivalent
Bracing recommended?
Read this first. This is a planning estimate only. It assumes standard annealed glass with a safety factor of about 3.8. For large or deep tanks, use tempered or laminated glass and get a professional structural calculation. Build only with aquarium-safe 100 percent silicone and leak-test before adding fish, because a panel or seam failure can flood the room.
Supplies for a DIY build
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How Aquarium Glass Thickness Is Decided
The force that wants to push your aquarium apart is water pressure, and water pressure depends on depth. A panel near the bottom of a 24-inch-deep tank carries far more outward force than the same panel in a 12-inch-deep tank, regardless of how long either tank is. That is why glass thickness is set primarily by water height. The table this calculator uses follows the common hobby guideline: water up to 12 inches deep uses about 6 mm glass, up to 16 inches uses 8 mm, up to 20 inches uses 10 mm, up to 24 inches uses 12 mm, up to 30 inches uses 15 mm, and anything taller than 30 inches should use 19 mm glass or a proper engineered design. These figures assume standard annealed glass with a safety factor of roughly 3.8, which is the cushion that keeps a tank intact even with small flaws in the glass or an imperfect bond.
Why Length Drives Bracing, Not Thickness
Length does not change the base thickness much, but it changes how far a panel will flex. A long front pane behaves like a wide, thin beam under load, and the middle bows outward. The longer the unsupported span, the more it deflects, and that deflection puts stress on the silicone seams at the corners. As a working rule, tanks longer than about 36 inches benefit from a top brace, and many builders add Euro-bracing, which is a glass rim bonded around the inside top edge of the tank. Bracing ties the long panels together so they cannot bow apart, dramatically lowering the strain on both the glass and the seams. This calculator flags a bracing recommendation when your length crosses that threshold, but on very large tanks a center brace or a full top with a viewing opening may be needed too.
Annealed, Tempered, and Laminated Glass
Annealed glass is ordinary glass. It can be cut and drilled, it is the basis for the thickness numbers above, and it breaks into large sharp pieces. Tempered glass is heat-treated to be four to five times stronger and breaks into small, relatively blunt fragments, which is why it is used for the bottoms of many factory tanks. The catch is that tempered glass cannot be cut or drilled after it is made: doing so releases the internal tension and shatters the entire panel instantly. If you want a drilled overflow or a bulkhead fitting, either order the holes before the glass is tempered or use an annealed bottom. Laminated glass bonds two layers with a plastic interlayer and holds together even when cracked, which is a safety feature on very large display tanks. Always confirm what a stock tank is made of before you ever bring a drill near it.
Build It Right, or Buy It
For most standard sizes up to around 75 gallons, a factory tank is usually cheaper and safer than a DIY build once you total the glass, silicone, and the cost of getting it wrong. DIY earns its place when you need unusual dimensions, a very large custom display, or a specific look you simply cannot buy. If you do build, treat the silicone as the real structural element: use only 100 percent silicone that is labeled aquarium-safe, with no added mildew or antifungal agents, since those additives are toxic to fish. Clean every bonding surface with acetone, lay an even bead, tool it, and give it a full cure of about a week before the tank holds water. Then leak-test it somewhere a spill does no harm, like a garage or outdoors, for a full day before it ever goes on a stand in your living room. A glass aquarium failure is not a slow drip, it can empty a hundred-plus gallons onto your floor in minutes, so when a build is large, deep, or you are unsure, pay for a professional calculation.
Keep going: finish planning your build.
Frequently Asked Questions
What thickness of glass do I need for an aquarium?
Glass thickness is driven mostly by water height, not by tank length or total volume, because the deeper the water the more pressure pushes outward on the panels. As a planning guide, water up to 12 inches deep uses about 6 mm glass, 16 inches needs 8 mm, 20 inches needs 10 mm, 24 inches needs 12 mm, 30 inches needs 15 mm, and anything taller wants 19 mm or professional engineering. This calculator returns both the millimeter and inch figure for your water height.
Why does water height matter more than tank length?
Water pressure increases with depth, so a tall narrow tank can put more strain on its panels than a long shallow one of the same volume. The bottom edge of a deep panel carries the most force, which is why the height-based table is the right starting point. Length still matters for bracing, since a long unsupported panel will bow in the middle even when the glass is thick enough, but height sets the base thickness.
What is the difference between annealed and tempered glass?
Annealed glass is standard glass that can be cut and drilled, and it breaks into large sharp shards. Tempered glass is heat-treated to be four to five times stronger and shatters into small blunt pieces, which is safer. The thickness numbers here assume standard annealed glass with a safety factor of about 3.8. Tempered glass lets you go thinner for the same strength, but it has a major catch on the bottom panel of drilled tanks.
Why can you not drill tempered glass?
Tempering locks the glass into a state of internal tension and surface compression. Cutting or drilling it after tempering breaks that balance and the whole panel explodes into small fragments instantly. If you want an overflow or bulkhead, the holes must be cut before the glass is tempered, or you must use an annealed bottom panel. Always confirm whether a stock tank uses tempered glass before attempting any drilling, since most commercial tanks have a tempered bottom.
When should I just buy a tank instead of building one?
For most standard sizes up to about 75 gallons, a factory tank is cheaper and safer than a DIY build once you count glass, silicone, and the cost of mistakes. DIY makes sense for unusual dimensions, very large custom builds, or when you want a specific look you cannot buy. If you do build, use only aquarium-safe 100 percent silicone, give it a full cure, and leak-test outdoors or in a garage for a day before it ever holds fish.
What silicone should I use for a DIY aquarium?
Use only 100 percent silicone labeled aquarium-safe or as a clear sealant with no added mildew inhibitors or antifungal agents, since those additives are toxic to fish. Avoid kitchen and bath silicone unless it specifically states it is safe for aquariums. Clean every bonding surface with acetone, lay an even bead, tool it smooth, and let it cure fully, usually about a week, before filling. The silicone joint, not the glass alone, is what holds the water in.
Do I need bracing on top of my tank?
Long tanks need bracing because the long front and back panels bow outward under water pressure, and the deflection grows with length. As a rule, tanks longer than about 36 inches benefit from a top brace or Euro-bracing, which is a glass rim bonded around the inside top edge. Bracing dramatically reduces bowing and the stress on your silicone seams. This calculator flags when your length suggests bracing is recommended.