At least three to five platies should be kept together. Platy fish are shoaling fish. They may not form a close-knitted group like schooling fish, but they still seek safety and comfort in numbers. A small group of three to five platies will be a great starting point for beginner fishkeepers with limited space.
Just ensure the tank doesn’t get too overcrowded. As a general rule, an inch of fish requires a gallon of water in the tank. Because platies can reach up to 2.5 inches when matured, each fish needs two to three gallons of water to live comfortably.
Also, because platies are livebearers, keep in mind that male platies will constantly want to mate. This might stress and tire out your female platies. To prevent this from happening, you should maintain a 2:1 ratio of female to male platies. Alternatively, you can keep only female platies.