people next door are moving and said i could have some old fish stuff that was their sons, cool! anyway the tank is roughly 30-12-12 inches.

it'll be a 20gallon long tank.

yes around 20gallons. which will house 2 goldfish

thanks

I calculate your tank volume to be 17.6747 US gallons. Don't forget to subtract the volume of any substrata or ornaments that you may place in the tank. This will of course reduce the water volume further. Also of course, the level of the water below the top of the tank.
For example, if you have 1" of substrata and the level of the water in your tank is 1" below the top, your tank will hold 14.9346 US gallons of liquid.

Here is a calculator for tank size
Tank Calculators

this is a common size, the 20 gallon long. an even more common size is the 29 gallon which is identical except 18" high instead of 12. You tank is good for two fancy fish or a single comet.

a 20 gallon is good for two goldfish for now but you will have to upgrade to a 30 gallon and if you get another goldfish you will have to upgrade to a 40 gallon, they grow fast and need room. I have learned this i am buying my third tank for my golfish, if i knew this at the beginning i would have gone with a 40 gallon from the start and ssaved some money, but oh well now i have a 20 gallon for a community tank.

To solve for volume of an aquarium:

In FEET!

Length x Width x Height x 7.5 = gallons of an aquarium