You can either get it at your physicians office; usually primary care physicians are very well qualified or very well equipped. They love to share that information with you. Also you can go online and there are a number of BMI calculators. Probably the best one is to go on Google and one of the sites that I like to use is from the NIH, and you simply put in your height and your weight in either the metric system or the U.S. system, and then it will calculate your BMI for you.