We’ve posted this before, but because we constantly find ourselves using it, we’ll post it once again. To quickly calculate the volume of any aquarium in gallons, just use this simple formula. Multiply the length by the width by the height of the aquarium, then divide by 231. This should give you a good rough estimate of how much water a particular aquarium can hold, but keep in mind that tanks usually aren’t filled to the top and things like sand and rocks displace some of that water. To demonstrate, here’s an example. A typical 180 gallon aquarium has dimensions of 72″L x 24″W x 24″H. Doing the multiplication, that’s a total of 41,472 cubic inches. Divide that number by 231, and you’re left with 179.53 gallons. So, not completely 180, but close enough to be called such.