An average indoor adult cat needs about 50-70 kcal per kg of body weight daily. A typical 4kg cat needs approximately 200-250 kcal per day. Kittens need more, seniors slightly less.
Dry food is calorie-dense (350-400 kcal/100g) while wet food is mostly water (70-100 kcal/100g). Mixing both provides balanced nutrition and increases water intake, which is important for urinary health.
You should be able to feel your cat's ribs with light pressure. If you can't feel them at all, your cat may be overweight. Aim for slow weight loss of 1-2% per week by feeding at the MER for their ideal weight.