body mass index tool

Why is BMI important?

Having a BMI outside the healthy or normal weight range has been shown to put you at increased risk of health conditions such as knee and hip arthritis, diabetes, heart disease and stroke. As shown in the table below, the health risks associated with excess weight increase dramatically with increasing BMI. 


classification BMI (kg/m2) risk of co-morbidities and related disease
underweight less than 18.5 low (but possibly increased risk of other clinical problems)
normal range 18.5 to 24.9 average
overweight 25.0 to 29.9 increased
obese I 30.0 to 34.9 moderate
obese II 35.0 to 39.9 severe
obese III 40.0 or greater very severe


Use the BMI calculator below to assess your BMI

Height cm ft in metric/imperial
Weight kg st lb metric/imperial

Note: The use of BMI does have some limitations as it does not distinguish fat mass from lean muscle mass nor does it reflect fat distribution. In some instances BMI can be influenced by age, gender and ethnicity and it is recommended that it be combined with a measure of fat distribution e.g. waist circumference in the clinical setting.