Aquarium glass thickness depends on water height more than gallons. Using annealed float glass at the hobby-standard safety factor of 3.8, a 10 gallon needs at least 3/16 inch (5 mm), a 55 or 75 gallon about 21 inches tall needs 3/8 inch (10 mm), a 125 gallon needs 1/2 inch (12 mm) and a 180 gallon needs 5/8 inch (15 mm). Rimless tanks should go one step thicker. The chart, formula and seam sizes are below.
Aquarium glass thickness is set by a single engineering question: how much does the panel deflect (bow outward) under hydrostatic pressure, and is that deflection within the safe limit for the glass and silicone seam?
The industry-standard formula derives from plate bending mechanics for a panel supported on four edges:
t = SQRT( (Beta x p x b^4) / (Sigma_a x SF) )
Where:
You do not have to calculate this by hand. The chart below pre-solves it for common tank sizes at standard safety factors.
Thicknesses below assume annealed float glass at SF=3.8, which is the hobby standard. Use these as MINIMUMS. Going one step thicker is always safer and rarely costs much more.
"Braced" means the design requires a center brace or full eurobrace on top. Without bracing, that panel is too tall for the listed thickness.
Float glass. Standard soda-lime glass produced by the float process (molten glass on a bath of molten tin). 99% of tank manufacturing uses float. Has a slight green tint from iron oxide impurities, visible from edge-on or in thick panels.
Low-iron glass. Float glass with reduced iron content (under 0.01% Fe versus ~0.10% for standard). Produced by Pilkington as Optiwhite, Guardian as Ultraclear, or AGC as Krystal Klear. Optical clarity is significantly better - no green tint, especially noticeable on rimless tanks viewed from the side. Same structural strength as standard float. Cost premium of 30-60% per square foot.
Tempered glass. Float or low-iron glass that has been heat-treated to ~1150 F and rapidly cooled, putting the outer surfaces in compression and the inner core in tension. The compression makes tempered ~4x stronger than annealed. Critical caveat: tempered glass cannot be cut, drilled, or ground after manufacture. Any attempt causes it to shatter.
What this means for aquarium use:
If you want to drill a tank for a bulkhead, the panel you drill MUST be annealed. Drilling tempered glass shatters it into thousands of pieces.
Three methods, in order of reliability:
A 75-gallon tank with 21-inch water depth and a 75-gallon tank with 17-inch water depth (e.g. shallower 75-gallon "long" variant) have very different glass requirements. The taller water column generates more hydrostatic pressure at the base, requiring thicker glass.
Hydrostatic pressure scales linearly with depth: 0.0361 PSI per inch. A 21-inch tank has 0.758 PSI at the bottom. A 30-inch tank has 1.083 PSI - 43% more pressure. This is why a 240-gallon tank with 30-inch water column needs 3/4 inch glass while a 240-gallon shallower "wide and shallow" reef tank with 18-inch water column may need only 1/2 inch.
When sizing replacement glass for a custom build, the height of the water column is the most important number to give your glass shop, more important than total volume.
A top brace (eurobrace, center brace, or full perimeter rim) reduces the effective span of the front and back panels. With a center brace, the front panel is no longer a single 48 x 21 inch panel - it is two 23 x 21 inch panels structurally. Smaller panel = less deflection = thinner glass acceptable.
For DIY builds, plan bracing into your design BEFORE ordering glass. The savings on glass cost often pay for the brace material.
The bottom panel sees less hydrostatic stress (water column above does not bow the bottom outward, gravity holds it in place) but it must support point loads from rocks and equipment. The bottom panel is usually:
The bottom panel is also the panel most likely to break under impact (dropped tools, magnetic cleaners). Building one step thicker on the bottom is cheap insurance.
Aquarium silicone bead width should be approximately equal to the glass thickness. A 3/8 inch glass tank should have a 3/8 inch silicone bead at each seam. Thicker bead is not stronger - it actually carries less load because more silicone means more compliance.
Glass pricing at typical 2026 US glass shops, per square foot, cut to size:
For a 75-gallon rimless build (1/2 inch low-iron, all six panels polished): expect $400-650 in glass alone before silicone and labor.
Maybe. Most off-the-shelf tanks are built at or near safety factor 3.8 minimums. They work for decades when stand support and bracing are correct. Watch the panel for visible bowing under load - more than 1/4 inch of outward deflection at the centerline of a side panel is a warning sign. Tanks built below SF 3.0 do fail, especially when stand support degrades.
For freshwater planted or display tanks where viewing matters, yes - low-iron transforms the visual experience. For sump glass, frag tanks, or back-panel-painted tanks where the back is not viewed, no - standard float is the same strength at half the cost.
Brands target different safety factors, and the safety factor sets the glass thickness. Most off-the-shelf tanks are built at or near the 3.8 hobby minimum, while premium and rimless builds often use a higher factor such as 5.0 and thicker glass, which adds cost and weight. When comparing tanks, ask each maker for the panel thickness and whether any panel is tempered.
Only if the panel is annealed, not tempered. Verify with the polarized sunglasses test. Drilling tempered glass causes immediate shattering. For annealed glass, use a diamond hole saw with constant water flow, low RPM (300-500), and light pressure. See our DIY plumbing guides for the full procedure.
Turtle tanks see additional impact load (turtles bumping the glass). Use one step thicker than the chart minimum for the tank size. A 75-gallon turtle tank should have 1/2 inch glass minimum. That is one step above the 3/8 inch (10 mm) float minimum the chart lists for a standard 75 gallon with a 20 inch water column.
Replace with the same thickness as original to maintain structural balance. Going thicker on just one panel creates stress concentration at the seam where the thinner panels meet the thicker one. Going thinner is unsafe by definition. Match the glass type too: tempered glass cannot be cut, drilled or ground after manufacture, so a tempered replacement panel has to be ordered at its final size.