BMI Calculator

Body mass index is a measure of body fat. It’s common usage is within the health industry to determine whether a person is healthy or not. BMI applies to both adult men and women and is the calculation of body weight in relation to height.


Body Mass Index formula

The formula for Body Mass Index was devised in the 1830s by Belgian mathematician Adolphe Quetelet. It is universally expressible as kg/m2.

The first formula we’ve listed below is the metric formula, using kilograms and meters. The second one is the English imperial formula, which uses units of pounds and inches.

Metric BMI Formula

BMI = weight (kg) ÷ height2 (m2)

Imperial BMI Formula

BMI = weight (lb) ÷ height2 (in2) × 703


BMI Categorization

The statistical categories below are based on Body Mass Index scores. These apply to adults of age 20 years and upwards. The World Health Organisation (WHO) regards a healthy adult Body Mass Index to be between 18.5 and 25.


BMI BMI Category
Less than 15 Very severely underweight
Between 15 and 16 Severely underweight
Between 16 and 18.5 Underweight
Between 18.5 and 25 Normal (healthy weight)
Between 25 and 30 Overweight
Between 30 and 35 Moderately obese
Between 35 and 40 Severely obese
Over 40 Very severely obese


BMI remains controversial

It is a common argument that the results Body Mass Index measurements provide are too general and do not consider the gender, build, age or ethnicity of a person. For example, professional athletes are often considered overweight or obese when using Body Mass Index measurements. This is due to their muscle content, which weighs more than fat.

As the age of people increases their bone density decreases. Thus, they may seem to have a weight within the normal BMI range. Their measurement actually needs to be scaled-down to reflect this. Alternatives to Body Mass Index do exist for those who consider it as an inaccurate measurement tool.

Always speak to a Doctor or health professional for advice and guidance if you are concerned about your weight.