while calculating tank sizes for fish (aside from some specific species), ... i've arbitrarily decided upon 10 gallons per inch, ... a fish with a 6" adult size is generally listed as 55 gallon tank min. (this is my thinking)
great gallons per inch, ... but gallons are volume and not size, ... a tank could be short or tall, and this would change the area of the tank base, ... and in turn change how much room the fish has to move around in.
i have heard "so long as the fish can move around comfortably"
now i'm going to ask what appears to be a simple silly question, ... "what does this mean"
-a fish at a 6" length
-is 8" comfortable to move around in, or 10", or 12", or 18" ?
(going by the short side of the tank)
tank sizes have a general typical shape, ... but ... i get curious about custom tanks, ... would suck to build a tank and think "hey, this fits the numbers, but the fish is not comfortable at all" :(