An Introduction to BMI

Body Mass Index (BMI) is a physical measurement used to assess an individual's total amount of body fat. 
BMI is calculated by dividing your weight in Kilogram (kg) by your height in metres squared (m2). BMI is expressed as kg/m2.

Body Mass Index (BMI) measures body fat, using a formula based on weight and height. BMI is applicable to both adult women and men.

Calculate your BMI using the calculator below.   Enter your weight and height using Kilograms and Centimetres. Click on "Calculate" and your BMI will appear to the left of the button.

BMI Categories:

• Underweight = <18.5
• Normal weight = 18.5 - 24.9
• Overweight = 25 - 29.9
• Obesity = BMI of 30 or greater

What Does Your BMI Mean?

The BMI scores give an indirect measure of body fat. Depending on the BMI value calculated you may be underweight, normal weight, overweight or obese. The cut off values are as follows:

Table 1: BMI Cut-Off Values

Why are BMIs Useful?

BMI is a simple, inexpensive screening tool used to identify possible weight problems for both adults and children. A BMI measurement is useful to assess who needs further testing to identify health risks such as heart disease . Individuals at risk will need further assessment. Assessments may include skin fold thickness test, diet, and physical activity level, family history and other appropriate health screenings.

What are the Limitations of BMI?

Listed below are limitations associated with BMI:

• BMI varies by age, sex and race hence one's BMI can only be compared to those of same sex, age and race.
• BMI does not differentiate between muscle and fat and will therefore underestimate in some and overestimate for others e.g. An athlete may have a high BMI because of greater amount of muscle rather than fat.
• Disabled or elderly people have less muscle mass and therefore will have a lower BMI. This does not necessarily mean that their BMI is normal or underweight.
• Pregnant women will also have a higher BMI because of increased weight associated with pregnancy but not necessarily due to increased fat and hence BMI will overestimate body fat in this case.
• BMI does not differentiate between body fat distribution and since fat around the waist ("apple" body shape) is more dangerous than that around the hips ("pear" body shape) this will not be picked up by BMI
• We recommend that you consult your health care giver for other physical measures that may need to be used along with BMI for assessing health risks associated with obesity.

Other Measures of Obesity