The suitable thickness of PVC flooring for a gym depends on the specific areas within the gym and the types of activities that will take place there. 

Group Exercise Studios: Studios where group exercise classes are held, such as aerobics, dance, and yoga, may benefit from PVC flooring with a slightly thicker profile to provide extra cushioning and shock absorption during high-impact movements. A thickness of around 4.5mm to 8mm is often suitable for group exercise studios.

General Gym Areas: For general gym areas with mixed-use, a thickness of around 4.5mm to 6mm is usually sufficient to provide a comfortable and durable flooring surface for a variety of activities, including stretching, warm-ups, and cool-downs.

It's important to consider factors such as the specific requirements of each area, the types of equipment used, the frequency of use, and the expected foot traffic when determining the appropriate thickness of PVC flooring for a gym. Additionally, ensure that the PVC flooring chosen meets relevant safety standards.