20 gallon tank measurements not possible

[SeeFu]

So i decided to measure my tank dimensions and I get 30.0625 width, 12.25 depth. take away the thickness of glass at 1/4 per panel and i end up w/ 29.5625 width and 11.75 depth. with those dimentions that would mean that the tank would need to be 13.3" tall to get to 20 gallons. My tank is only around 12" tall. I've also noticed my 125 gal has the same issue. the actual measured dimensions always come up w/ less volume than advertised. am I doing something wrong here when I do my math?

 

[JoshH]

So i decided to measure my tank dimensions and I get 30.0625 width, 12.25 depth. take away the thickness of glass at 1/4 per panel and i end up w/ 29.5625 width and 11.75 depth. with those dimentions that would mean that the tank would need to be 13.3" tall to get to 20 gallons. My tank is only around 12" tall. I've also noticed my 125 gal has the same issue. the actual measured dimensions always come up w/ less volume than advertised. am I doing something wrong here when I do my math?

Not doing anything wrong, it's pretty common in the industry to round up Gallon wise to a round number. Heck waterbox counts the entire sump space in there volume and the thing runs at half capacity when set up.

 

[Sailingeric]

sounds like you have a 20 gallon long and even using the standard dimensions, of 30x12x12 which I assume is the outside of the tank, is 4320 cubic inches or 18.7 gallons. My 75 gallon DT using the 48" x 18" x 21" measurement is actually 78.5 gallons.