Buyers often size an aquarium window from the tank’s litres. The sheet does not care about litres. It cares about two numbers: how deep the water sits above the window sill, and how far the unsupported panel spans.
The two inputs
Hydrostatic pressure rises linearly with depth. At 1 m the load is about 10 kPa; at 4 m it is about 40 kPa. Deflection, though, grows with roughly the fourth power of span for a fixed thickness, which is why doubling the window width can multiply the required thickness several times.
Worked numbers that hold up in service
These are cast-acrylic figures used on built tanks, with a deflection limit around span/100 and a safety factor of at least 2 on the yield stress:
- 1,200 mm depth, 1,500 mm span → 20 mm
- 2,000 mm depth, 2,000 mm span → 30 mm
- 3,000 mm depth, 3,000 mm span → 60 mm
- 4,000 mm depth, 3,000–4,000 mm span → 100–120 mm
A cylindrical tank is a different case: a curved panel carries load in compression around the circumference, so a 600 mm diameter cylinder can run much thinner than a flat window of the same depth. Do not apply flat-window numbers to a cylinder.
Where buyers get caught
The common error is measuring depth to the waterline instead of to the window sill. If the window top sits 300 mm below the waterline, that 300 mm still loads the panel. The second error is ignoring the frame: a panel held on a stiff rebate behaves differently from one on four bolts, and the bond absorbs part of the load only when the rebate is properly detailed.
The depth-to-thickness relationship for pool glazing is set out in acrylic pool window thickness, and the observation-window case in underwater observation window.
Frequently Asked Questions
Q: What thickness acrylic for a 2 m deep aquarium window?
A:Around 30 mm cast acrylic for a 2,000 mm span at 2,000 mm water depth, with a deflection limit near span/100. Wider spans grow quickly — a 3,000 mm span at the same depth moves toward 60 mm.
Q: Does tank volume decide acrylic thickness?
A:No. Thickness follows water depth above the window sill and the unsupported viewing span. Two tanks of the same volume with different window shapes need different sheets.
For aquarium panel drawings with water depth, viewing span and frame detail, email oversales@rpplexiglass.com and we will return a thickness and bond schedule.