BMI Calculator

BMI is a quick screening number used by clinicians as a starting point, not a verdict on your health. The results panel explains what the number does and does not tell you.

How to use the bmi calculator

Choose metric or imperial units.

Enter your weight and height.

Read your BMI, category and healthy weight range – it updates as you type.

Why use the Convert Now bmi calculator

Metric and imperial

Kilograms and centimetres, or pounds, feet and inches – switch with one tap.

Visual scale

See where you fall on the BMI scale, not just the number.

Healthy weight range

Shows the actual weight range for a healthy BMI at your height.

Private

Nothing you enter is uploaded or stored.

What the BMI number means

Body mass index divides your weight in kilograms by the square of your height in metres. The World Health Organization classifies adults as underweight below 18.5, healthy weight from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 and above. The formula was devised in the 19th century as a way of describing populations, and it survives because it needs only two measurements that anyone can take.

Where BMI gets it wrong

Because it uses only height and weight, BMI cannot tell muscle from fat. A rugby player and a sedentary person of the same height and weight get the same score. It also does not account for where fat is stored – abdominal fat carries more metabolic risk than fat on the hips – and the standard thresholds were derived largely from European populations, so several health bodies use lower cut-offs for people of South Asian descent. It is not designed for children, pregnant women or the very elderly. Waist circumference and waist-to-height ratio are useful companions.

Using the healthy weight range

The result shows the weight range that corresponds to a BMI of 18.5–24.9 at your height, in whichever units you selected. That range is often more useful than the index itself, because it turns an abstract number into a target you can actually act on – and it makes clear how wide the healthy band is.

Read the guide: What Is a Good BMI? Healthy Ranges Explained

This calculator provides general health information and is not medical advice, diagnosis or treatment. Individual needs vary with body composition, age, medication and medical conditions. Speak to a doctor or registered dietitian before making significant changes to your diet or exercise.

Frequently asked questions

How do I calculate BMI?

Enter your weight and height. BMI is weight in kilograms divided by height in metres squared; the calculator handles the unit conversion if you use pounds and feet.

What is a healthy BMI?

For most adults, 18.5 to 24.9 is classed as the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or above is obese.

Is BMI accurate for athletes?

Often not. Muscle is denser than fat, so muscular people frequently score as overweight or obese despite low body fat. Body composition measurement is more useful for them.

Does BMI work for children?

No. Children and teenagers are assessed with age-and-sex-specific percentile charts rather than the adult thresholds used here.

Is BMI different for men and women?

The formula and thresholds are the same, although women naturally carry a higher percentage of body fat at the same BMI.

Is my data private?

Yes. Your height and weight are used only in your browser and are never transmitted.