BMI is a way to quantify the amount of tissue mass (muscle, fat and bone) and then categorize the person as – underweight, normal weight, overweight, or obese.
BMI is defined as – body mass (in Kilograms) divided by the square of body height in meters. Thus the unit of BMI is kg/m2.
If pounds and inches are used, a conversion factor of 703 (kg/m2)/(lb/in2) must be applied.
Based on the BMI value your weight could be categorized as the following.
Underweight: Your BMI is less than 18.5.
Healthy weight: Your BMI is 18.5 to 24.9.
Overweight: Your BMI is 25 to 29.9.
Obese: Your BMI is 30 or higher.
In simple words BMI tells you for your height, what should be your ideal body weight.
Take an example.
Suppose your height is 5 feet and 6 inches (167 cm) and weight is 70 Kgs.
Then your BMI is 25.1 , which means you are overweight.
Suppose you bring down your weight to 65 Kgs.
Then you BMI becomes 23.3 and you would be in the ‘Healthy Weight‘ category.
Please see the below chart for better understanding.