BMI Calculator

What it measures

BMI (Body Mass Index) is a simple screening number calculated from your height and weight. It gives a broad indication of whether your weight falls in a range associated with good health for your height. It is not a direct measure of body fat, fitness, or overall health.

How it works

You enter your height and weight (metric or imperial). The calculator divides your weight in kilograms by the square of your height in metres (kg/m²) and places the result in one of the WHO adult categories: underweight, healthy weight, overweight, or obesity classes I–III. The whole process takes under a minute.

Tips for an accurate result

• 1Waist circumference adds important context — A waist measurement above 88 cm (35 in) for women or 102 cm (40 in) for men signals higher metabolic risk regardless of BMI. Measuring your waist is a useful companion check.
• 2Aim for gradual, sustainable change — If your BMI is outside the healthy range, even a 5–10 % reduction in body weight can meaningfully lower the risk of type 2 diabetes and heart disease, without needing to reach an 'ideal' BMI.
• 3Physical activity matters independently of weight — A moderately active person with a slightly elevated BMI may have lower cardiovascular risk than a sedentary person in the healthy BMI range. Fitness and weight are separate health levers.
• 4Speak to your GP before any major dietary change — If your result is in the underweight or obesity class II–III range, or if you have an existing health condition, professional guidance before making large changes to diet or exercise is strongly advisable.