Like any protein supplement, casein protein supplements are dosed in relation to dietary protein goals and how much dietary protein is consumed via other sources. Protein goals vary from person to person, but a general guide is:
If you are an athlete or highly active person currently attempting to lose body fat while preserving lean muscle mass, a daily intake of 1.5-2.2g/kg bodyweight (0.68-1g/lb bodyweight) would be a good target
If you are an athlete or highly active person, or you are attempting to lose body fat while preserving lean mass, then a daily intake of 1.0-1.5g/kg bodyweight (0.45-0.68g/lb bodyweight) would be a good target
If you are sedentary and not looking to change body composition, a daily target of 0.8g/kg bodyweight (0.36g/lb bodyweight) and upwards would be a good target
Supplementation of casein protein should be in the dose that is required to meet these ranges after dietary protein has been accounted for. If dietary protein has adequately reached these ranges, then protein supplementation is not required.
Individuals with obesity (having a BMI greater than 30 without significant levels of muscle mass) should not follow the above recommendations exactly as the state of obesity would overshoot requirements. In these instances, calculate your targets based upon what your weight would be assuming an overweight BMI.