how many gallons does a 24 1/2" BY 24 1/2" BY 18" fish tank hold?

Answer 1

Ok, assuming these are the INTERNAL dimensions - or that the glass thickenss is not important then proced as follows.

Note this also give a "full to the brim" answer, no space her for an air gap :)

24.5 x 24.5 x 18 = 10804.5 square inches
divide this be 1728 to give cubic feet = 6.25
US gallon = 0.13368 cubic feet, so: 6.25 / .013368 = 46.75 US gallons
divide by 1.2 to give "non US Gallons" = 38.96 (39)

So just under 47 US gallons or just under 39 UK gallons :)

Answer 2

That is roughly 25 gallons :-)

Answer 3

as much as it can until the water spills out over the top i guess