Calculate your Body Mass Index instantly in metric or imperial units. See your category, visualise where you fall on the BMI scale, and understand what the number means.
Calculate your Body Mass Index. Works in metric (kg/cm) and imperial (lbs/ft) units.
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese | 30 and above |
The metric BMI formula is: BMI = weight(kg) ÷ height(m)². For imperial: BMI = (weight(lbs) ÷ height(in)²) × 703. The World Health Organisation defines normal weight as a BMI between 18.5 and 24.9.
BMI is a useful screening tool but has known limitations — it cannot distinguish between muscle and fat mass, and does not account for age, sex, or body fat distribution. Use it as a starting point for conversation with a healthcare professional, not as a definitive health verdict.
Body Mass Index is a simple screening measure that relates your weight to your height. It was designed to flag whether an adult's weight sits in a range associated with lower health risk, and it does this well across large populations. The World Health Organisation classifies a BMI below 18.5 as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 or above as obese.
BMI is popular because it needs only two measurements and no equipment beyond a scale and a tape measure. That simplicity is also its main limitation. BMI cannot tell the difference between muscle and fat, so a very muscular athlete may register as overweight despite low body fat. It also does not account for where fat is stored, or for differences related to age, sex, and ethnicity. For these reasons it is best used as a starting point rather than a diagnosis.
A single BMI reading is most useful when combined with other information — waist measurement, activity levels, diet, family history, and how you feel day to day. Trends over time often matter more than one number: a gradual shift in either direction can be more informative than where you sit on the scale today. If your BMI falls outside the normal range, it is worth discussing with a healthcare professional who can interpret it in the context of your overall health.
For example, an adult who weighs 70 kg and stands 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which sits in the normal-weight range. The same 70 kg at 1.60 m gives a BMI of 27.3 — overweight — showing how strongly height affects the result. If your number sits close to a boundary, a waist measurement or a chat with your doctor usually tells you more than the BMI figure alone.
Is BMI accurate for everyone?
No. BMI works well for populations but less well for individuals, especially very muscular people, older adults, and some ethnic groups. It is a screening tool, not a diagnosis.
What is a healthy BMI?
The World Health Organisation defines a normal-weight BMI as 18.5 to 24.9. Ranges can be interpreted slightly differently depending on age and ethnicity.
Does BMI measure body fat?
Not directly. It estimates whether your weight is in a healthy range for your height, but it cannot distinguish fat from muscle or show where fat is stored.