Aquarium Glass Thickness Calculator

Building your own tank? Enter its dimensions to get the glass thickness for the front, ends and bottom, rounded up to the sizes glass is sold in.

How many times stronger than the bare minimum the glass must be.
48 in 20 in 18 in
Front and back panels10 mmsold as 3/8 in · calculated minimum 9.4 mm
End panels8 mmcalculated minimum 6.1 mm

For a rimless float-glass tank 48 in long and 20 in tall, at a safety factor of 3.8, the front and back need glass at least 9.4 mm thick: buy 10 mm, the next stock size up. Most builders use the same thickness for all four sides and the bottom.

Bottom panel, on a flat, fully supported base
10 mm (same as the front)
Bottom panel, if supported only at its edges
12 mm (minimum 11.8 mm)
Bow in the middle of the front panel
0.3 mm
Water pressure at the bottom
4.98 kPa (0.72 psi)
Tank volume, brim-full
74.8 US gal (283 L)

This is a guide for planning, not an engineering certificate. It assumes new float glass with polished edges, no chips or scratches, good silicone joints and a level, flat base. Tempered glass and acrylic follow different rules.

What to work out next

Tank weightWeight with this glassReal water volumeInside volume with this glass

How glass thickness is calculated

Water pressure grows with depth, so the glass at the bottom of a panel carries the most load. The thickness needed depends far more on the tank's height than on its length.

Each side panel is treated as a flat plate held along three edges (bottom and both ends) and free at the top, which is how a rimless, unbraced tank behaves:

Thickness = √( β × p × H² ÷ σ )p = water pressure at the bottom (9.81 kPa per metre of height). H = height. σ = allowed stress = 19.2 N/mm² ÷ safety factor. β = a plate constant that depends on length ÷ height.
Length ÷ height 0.5 0.67 1.0 1.5 2.0 2.5 3.0 or more
β 0.085 0.116 0.16 0.26 0.32 0.35 0.37

Worked example. A tank 120 cm long and 50 cm tall, safety factor 3.8. Length ÷ height = 2.4, so β ≈ 0.344. Pressure at the bottom is 0.0049 N/mm². Allowed stress is 19.2 ÷ 3.8 = 5.05 N/mm². Thickness = √(0.344 × 0.0049 × 500² ÷ 5.05) = 9.1 mm, so use 10 mm glass.

The result is then rounded up to the next thickness that float glass is sold in: 4, 5, 6, 8, 10, 12, 15, 19 or 25 mm.

What the safety factor means

Glass is strong but unpredictable: tiny scratches and edge chips, invisible to the eye, decide where it breaks. A safety factor of 3.8 means the glass is designed to carry 3.8 times the load it will actually see. It is the figure most home builders and published guides use. Do not go lower unless the tank has a full frame or bracing designed by someone who knows the trade, and go higher for tanks in public places or homes with small children.

Factory tanks often use thinner glass than this calculator suggests. They can, because their plastic or glass frames and centre braces stop the top edge from bowing, and because their glass and joints are made under controlled conditions.

The bottom panel

A bottom panel resting on a flat, level stand with a foam mat carries very little bending stress, so the same thickness as the front is the normal choice. If the base is supported only around its edges, as on some framed tanks and open-topped stands, it must span the gap like a bridge and needs to be much thicker: the calculator shows that figure too.

Before you build

This calculator is a planning guide based on standard plate formulas. It cannot see the quality of your glass, edges or silicone work. For tanks taller than 30 inches (76 cm) or longer than 8 feet (244 cm), or wherever a failure could injure someone, have the design checked by a professional tank builder or structural glazier. Tempered glass and acrylic follow different rules and are not covered here.

Common mistakes

  • Sizing by tank length. Height drives pressure: a tall tank needs thicker glass than a long one of the same volume.
  • Using glass with raw or chipped edges. Have every edge ground or polished: cracks start at edge flaws.
  • Building on an uneven base. A twist of a millimetre or two concentrates stress in one corner. Use a flat board and a foam mat under rimless tanks.
  • Using bathroom silicone. Only 100% silicone sold as aquarium-safe, with no mould inhibitors, is suitable.
  • Filling too soon. Let silicone cure for the time the maker states, usually at least a week for large tanks.

Questions and answers

How thick should aquarium glass be?

It depends mostly on height. As a rough guide for rimless tanks at a safety factor of 3.8: up to 30 cm (12 in) tall, 5–6 mm; 40 cm (16 in), 8 mm; 50 cm (20 in), 10 mm; 60 cm (24 in), 12–15 mm. Enter your exact dimensions above.

What glass thickness for a 55 gallon tank?

A 48 × 13 × 21 inch tank calculated as rimless at a safety factor of 3.8 needs 10 mm (3/8 in) glass. Factory 55-gallon tanks use 6 mm (1/4 in) glass because their frames and centre brace support the top edge.

What is a safe safety factor for aquarium glass?

3.8 is the standard for home-built, unbraced tanks. Lower figures are only for braced or framed designs; higher figures add margin for large tanks or public places.

Is 6 mm glass enough for my aquarium?

For rimless tanks up to roughly 30–35 cm (12–14 in) tall and 60–75 cm long, usually yes. Taller tanks need thicker glass. Check your dimensions in the calculator.

Does the bottom glass need to be thicker?

Not when the base sits flat on a level, fully supporting stand with a foam mat. It does when the base is held only around its edges.

Can I use this for acrylic?

No. Acrylic is less stiff than glass and bows more, so it is sized by deflection rather than strength. Use the acrylic maker's own tables.

Sources

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