Juwel Vision 260 - actual volume?

Icemist Member Posts: 10
I was talking to a friend about the Juwel Vision 260 and am struggling to work out the litres that the tank holds. The website states 260 litres / 68 us gallons with the tank measuring 121 cm long x 46 cm wide x 64 cm high.
But when I calculate the actual volume it comes to 356 litres or 94 us gallons.
Why? Is there something I am missing when calculating this?