Aquarium Glass Thickness Calculator
This aquarium glass thickness calculator estimates the minimum safe glass for a tank panel from the panel width, the water depth and a safety factor you choose. Water pressure rises with depth and pushes outwards on the glass, hardest right at the bottom, so the panel that has to be sized is the one holding the deepest water, usually the front or a side. The tool treats that panel as a strip spanning its shorter dimension, simply supported around the edges, and works out the thickness needed to keep the bending stress in the glass below a safe limit. That limit is the breaking stress of glass divided by your safety factor, which is why a bigger safety factor calls for thicker glass. It then rounds up to the next standard glass size, so you get a practical figure you can actually order. This suits hobbyists planning a DIY build, checking a second-hand tank, or sanity-checking a quote, and it deliberately errs on the thick side by ignoring any bracing, which always helps rather than hurts. Enter your panel width and fill depth in millimetres, pick a safety factor, and read the recommended thickness. A worked example and the formula are set out below. For a large, tall or public-facing tank, treat this as a first estimate only and have the design confirmed by a qualified glazier.
At a safety factor of 3.8, a 900 mm x 450 mm panel needs at least 7.98 mm of glass, so 8 mm is the recommended standard thickness.
Assumes a single flat annealed panel with no bracing, water density 1,000 kg/m3, gravity 9.81 m/s2 and a glass breaking stress of 40 MPa. Bracing and tempering allow thinner glass. Estimate only: have large or tall tanks checked by a professional.
How it works
The pressure of still water at a given depth is density times gravity times depth, so a tank filled to 0.45 m has a base pressure of 1,000 x 9.81 x 0.45, about 4,415 pascals or 4.41 kPa. The glass panel bends under that load. Modelling the panel as a strip that spans its shorter side and is simply supported at both ends gives a maximum bending stress of 0.75 times the pressure times the span squared, divided by the thickness squared. Setting that equal to the allowable stress, which is the glass breaking stress of 40 MPa divided by your safety factor, and solving for thickness gives t = b x square root of (0.75 x pressure / allowable stress), where b is the shorter span in metres. The answer is then rounded up to the next standard glass size: 4, 5, 6, 8, 10, 12, 15 or 19 mm.
Worked example
Take a panel 900 mm wide holding water 450 mm deep, with a 3.8 safety factor. The shorter span is 450 mm, or 0.45 m. Base pressure is 1,000 x 9.81 x 0.45 = 4,414.5 Pa. Allowable stress is 40,000,000 / 3.8 = 10,526,316 Pa. The required thickness is 0.45 x square root of (0.75 x 4,414.5 / 10,526,316) = 0.45 x 0.01773 = 0.00798 m, which is 7.98 mm. Rounding up to the next standard size gives 8 mm glass, which matches common practice for a tank this size.
Related calculators
- Hydrostatic Pressure Calculator: water pressure at depth.
- Tank Volume Calculator: capacity in litres.
- Cuboid Volume Calculator: box volume from dimensions.
- Buoyant Force Calculator: upthrust on submerged objects.
- Pressure Calculator: force over area.
- Glass Weight Calculator: what the pane weighs once you have settled the thickness.