Platies get as big as 2.5 inches long when mature. Female platies tend to be bigger than males. Female platy fish can grow to be 2.5 inches in length, while male platies only grow to be 1.5 inches. Platies will reach their maximum size at just around six months of age.
Generally, an inch of fish requires a gallon of water in the tank, so each platy needs two to three gallons of water to thrive. Also, because they’re shoaling fish, you should keep at least three to five platies together.
You’ll need a 15-gallon tank or bigger to keep your platies happy.