SIZE: APPROX. 12.5" X 18.75" . PLEASE MEASURE YOUR TANK PRIOR TO PURCHASE!!! THIS WILL ONLY FIT A STANDARD 29GALLON OR STANDARD 55 GALLON!! Please watch installation video before installing for easy step by step instructions. Finally an aquarium divider you can trust! Fin Friends patented aquarium divider was designed to finally solve the problem of separating aggressive fish, sick fish, baby fish (Not for babies under 1") or just different species of fish all in the same tank without needing extra heaters or filtration. These dividers were designed with suction cups that attach on both the top and bottom of the tank that stop even aggressive fish from bullying their way through. We have tested this divider with 1inch fry for 2 months now without any escaping. The design features two side rails that attach to a plastic mesh with push pins, making it impossible for the mesh to come free. The side rails attach to the side of the tank with 2 suction cups on each side, and a top and bottom rail are added for extra support. After raising many fish ourselves, we needed a way to divide our fry without having to worry about the divider failing. We created this divider and know it works because we use it ourselves. This Divider will fit most 29 gallon and 55 gallon tanks. It will not fit tanks that are wider than 12.5 inches or shorter than 18.75 inches. Please measure your tank before purchasing!