BMI Calculator

BMI (Body Mass Index) is a simple number calculated from your height and weight. It estimates whether your body weight is in a healthy range for your height. BMI is useful for population-level screening, but it does NOT directly measure body fat percentage, muscle mass, bone density, or fat distribution. For example, a muscular athlete may show a high BMI even with low body fat, while someone with normal BMI may still have high belly fat. Use BMI as a starting point, not as a full diagnosis.

BMI is calculated using the formula: BMI = weight(kg) ÷ height(m)². If you use pounds and inches, the formula is: BMI = 703 × weight(lb) ÷ height(in)². Example: if you are 70 kg and 1.75 m tall, your BMI = 70 ÷ (1.75×1.75) = 22.9. This calculator automatically converts units and shows your category (underweight, normal, overweight, obesity) within seconds.

The WHO global classification defines six adult bands: Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese Class I 30–34.9, Obese Class II 35–39.9, and Obese Class III ≥40. These bands describe risk across populations, not the health of any one person — two people with the same BMI can have very different amounts of fat and very different metabolic health.

BMI cannot distinguish fat from muscle, bone, or fluid — a muscular athlete and a sedentary person of the same height and weight get the same number. It also says nothing about where fat is stored, even though abdominal fat carries most of the metabolic risk. The cut-offs were derived largely from European-descent populations, so risk rises at a lower BMI in many South and East Asian populations and at a higher BMI in some Pacific Island and Black populations. Use BMI alongside other measures like waist circumference, not on its own.

For many Asian populations, health risks like diabetes and heart disease can appear at a lower BMI than in Western populations, which is why the WHO Asia-Pacific (WPRO) report proposes lower regional cut-offs — available here as an optional toggle. The 2004 WHO Expert Consultation reviewed this evidence and chose not to change the global classification, instead adding 23 and 27.5 as extra public health action points, so these are additional reference points, not a replacement standard. Turn the toggle on if that regional context applies to you.