That has been the standard in aquarium building since the first tank was built.
Look at Custom Aquariums web site. They list the common standard gallon size, then the actual gallon volume. Some are different as much as 40 gallons. Just the way its always been.
Look at Custom Aquariums web site. They list the common standard gallon size, then the actual gallon volume. Some are different as much as 40 gallons. Just the way its always been.