BMI, short for body mass index, is a quick way to assess whether someone is underweight or overweight. The formula is not perfect, because it only uses height and weight and does not take into consideration the body's composition. Nevertheless, BMI is widely used as a screening tool because it can be figured quickly. According to the Center for Disease Control, the normal BMI range is from 18.5 to 24.9. Anything higher than this suggests the person is overweight.

Multiply your weight in stone by 14 to convert to pounds. For example, if you weigh 13 stone, you would multiply 14 by 13 to get 82.6 Kilogram.

Multiply your height in feet by 12 to convert to inches. For example, if you are 5 feet 8 inches tall, you would multiply 5.75 by 12 to get 69 inches.

Square your height in inches, i.e. multiply it by itself. So if you are 69 inches tall, you would get (69 x 69 =) 4,761.

Divide your weight by your height in inches squared. Continuing the example, you would divide 182 by 4,761 to get 0.0382272631800042.

Multiply the step 4 result by 703 to find your BMI. Finishing the example, you would multiply 0.0382272631800042 by 703 to get a BMI of 26.87.