Re: Actual gallons of water When aquarium sizes are advertized, the "volume" given is calculated from the external dimensions of the tank. Glass has thickness and this decreases the actual water volume. Also, in actual practice, you almost never fill the tank up to the very top. Just for comparison here's the calc's for my 180g tank:
72"x24"x24" = 41,472 cubic inches
41,472 / 231 (cubic inches per gallon) = 179.53 gallons.
But.... the glass is 1/2" thick, making the interior dimensions 71"x23"x23.5" = 38,376 cubic inches.
38,376 / 231 = 166.13 gallons.
Smaller tanks use thinner glass, but as a practical mater, I usually figure about 85% of stated volume when doing calculations. For a 180g tank that works out to about 153g. I round to 150g to make it easy.
A 20g aquarium would be 17g, etc. |