Required Calorie for Weight Loss. Required Calorie for Weight Gain. Based on your daily activity, age, etc. Body Fat Percentage Calculator. Body mass index (BMI) Calculator. BMI, is a value derived from the mass (weight) and height. Based on sex, it could be from Severely Underweight to Perfect to Severely Obese. It's like a quick way to calculate the perfect weight for you. Based on these calculations, you might need to take some precautions.