How do you caculate your BMI?

From WikiHow, you can calculate in pounds:

• Collect a few household materials to find your Body Mass Index (BMI): your bathroom scale; a yardstick; a pencil and paper and calculator.
• Weigh yourself on your clean bathroom scale.
• Measure your height in inches using the yardstick.
• Use the pencil, paper and calculator to perform the following BMI calculation:
  • Your height in inches and square the number (i.e. multiply the number of inches by the same number).
  • Divide your weight in pounds by the second figure (your height in inches squared).
  • Multiply that number by 703. The answer is your Body Mass Index.

Or you can let a BMI calculator do the math for you. You'll still need to know your precise height and weight, but you can use either English or Metric measurements in the calculator at the link to the Centers for Disease Control and Prevention's (CDC) BMI calculator, which is accessible by using the link further down this page. They have a calculator for adults and one for children and teens. Also see the related questions linked to this question for more information.

Note that BMI does not account for muscle mass. A short individual who has a large muscle mass may be considered obese by BMI calculations even though their body fat is low. Muscle weighs more than fat. Use the BMI as a guideline only, it is not health science.