Knowing your body mass index (BMI) is helpful if you are looking to lose weight, build muscle or want to see where your weight and height match up with everyone else. In order to figure out how to find your BMI you have to divide your weight in kilograms by how tall you are in meters. Once you have done that, you need to divide that number by your height in meters a second time.
So for an example, if your weight is 80 kilograms and you are 2 meters tall, you divide 80 by 2 and you get 40. Then you divide 40 again by 2 which gives you 20. So your BMI is 20kg/m2. There are also different websites that can help you calculate this as well.