The most commonly used method of assessing whether a person is normal weight, underweight, overweight or obese. Calculated by dividing the persons weight (in kilograms) by their height (in metres) squared. Also known as Quetelet's Index. For both men and women, underweight is a BMI below 18.5, acceptable weight is from 18.5 to less than 25, overweight is 25 and above but less than 30, and obese is 30 and over