Yepper. Volume is measured in a water based cubic equivalent (cu in, cc, etc.) The fluid oz size of the tank is based on fluid ounces of distilled water. (Except in Canada where they use the "Royal Gallon" and that's based on the queen's urine or some odd uint of measure). Things that float on water (alcohol, ducks, witches, etc.) will WEIGH less than pure water for an equivalent volume.