BMI stands for Body Mass Index. It is a simple method used to indicate body fat content and to classify underweight, healthy weight, overweight and obesity. Both height and weight measurements are required to calculate BMI. There are slightly different cut-offs for different ethnicities.
These are the cut-offs in the table below for underweight, normal range, overweight and obese classes I to III. BMI is used to estimate the proportions of a population in various weight status categories and is a less accurate estimate of body fatness at the individual level. There are many online calculators to calculate BMI, but it can also be calculated manually using the following formula:
Weight (kg) divided by height squared (m2).
For example, Lee weighs 78kg and is 180cm tall.
Lee’s BMI is:
78kg/1.8m2 = 24.1
The BMI cut-offs for adults as underweight, normal range, and obese are as follows:
Adapted from World Health Organisation (1995, 2000, 2004). BMI classification
The health risks associated with increasing BMI continue with each classification. However, there are some limitations with using BMI to measure disease risk.
BMI calculator Limitations
BMI is based on height and weight only. Therefore, it does not take into account age, sex, or body composition such as fat or muscle mass. Parameters also need to be adjusted for some ethnicities. Therefore, it is not always the most accurate indicator for health risk in some people. BMI often overestimates the amount of body fat in body builders, athletes, and pregnant women. It also underestimates the amount of body fat in the elderly where the proportion of fat is likely to be higher.