For what it's worth, a DuBro 8oz tank with a full load of fuel and a four inch piece of tubing coupling the vent to the supply so it didn't spill on my scales weighs 8.54 oz. The same tank empty weighs 2.29 oz. So the tank holds 6.25 oz of fuel by weight. There is a air gap as shown in the photo, you really can't get you tank completly full of fuel.

Don

Turn the photo on it's side.