ActiveAqua Reservoirs have stronger corners and are thicker all around than most other brands. Slightly concave sides to improve strength and avoid bowing.

Inside graduation to verify water level.

25 Gallon Reservoir - 30in x 30in x 13in
50 Gallon Reservoir - 39.5in x 39.5in x 13in
75 Gallon Reservoir - 46.5in x 46.5in x 13in
100 Gallon Reservoir - 53in x 53in x 13in