The thickness of the acrylic matters when shopping for a tank. When we are asked what is the "correct" thickness, the answer we give starts with "It depends", let's take a look at what you want.
Many fabricators use simple rules of thumb criteria such as if it is "X" inches tall then the walls need to be "Y" inches thick and the top needs to be "Z" inches thick. This simplistic approach often results in fabrications that are good enough but not elegant..
Acrylic tanks are systems. A quality tank build is not just one thing but everything. Many criteria need to be addressed, not just wall thickness. This is why almost every tank we sell is custom quoted and custom manufactured.
For example, take a tank 20 inches long by 14 inches wide and 36 Inches high with bent front corners. The total volume is approximately 44 gallons. Going by simple "rules of thumb", other companies would use 3/4" thick acrylic at this height. We have built many tanks similar to this using 1/2 inch material. The end result is a tank with minimal deflection (not to be confused with "bowing") and beautiful proportions. Made from 3/4 inch this tank would look awkward if not ugly.
This is an extreme but not unrealistic example and is used to emphasize "Design Matters" and simple rules of thumb are short cut answers.
What about that 8 foot high tank made from half inch acrylic?
Again, this is an extreme example to prove the points we discussed above. The image below is of that 8 foot high pressure testing tank for a medical device manufacturer. It does not have a top. It does not have a Eurobrace. It does not bow.
Each tank is different and all design criteria need to be addressed, not just wall thickness. Using simple rules of thumb is a short cut approach that may not result in a quality tank.