Most of the world calculates height and weight using the metric system. BMI charts are widely available based on English measurements -- pounds, feet and inches -- and automatic BMI calculators are all over the Internet. Even so, you can get a precise measurement of your own BMI if you calculate it yourself. Be aware that BMI does not correlate perfectly with how "fat" a person actually is -- it's just an estimate. If you have any concerns about your weight or BMI, ask your doctor.
Calculate your weight in kilograms by multiplying your weight in pounds by 0.45. For example, if you weigh 128 lb., do the following calculation: 128 lb. x 0.45 lb./kg = 57.6 kg.
Calculate your height in inches. For example, if you are 5 feet, 6 inches tall, you multiply 5 by 12, then add 6: You are 66 inches tall.
Convert your height from inches to meters, by multiplying your height in inches by 0.0254. In our example, 66 in. x 0.0254 m/in. = 1.6764 m.
Square your height in meters. This means to multiply that number by itself, to get your height in units called "meters squared": 1.6764 m x 1.6764 m = 2.81 meters squared.
Calculate your BMI by dividing your weight in kilograms by your height in meters squared. Our imaginary person would do her calculations this way: 57.6 kg / 2.81 meters squared = 20.5 BMI, which puts her in the "normal" range of BMI, neither over- or underweight.