BMI Calculator

What is BMI?

Body mass index (BMI) is a single number that compares your weight with your height. You get it by dividing your weight in kilograms by the square of your height in metres. The number is then read against fixed ranges that place an adult as underweight, normal weight, overweight or obese.

Doctors, insurers and public health agencies use BMI because all it needs is a weighing scale and a measuring tape. It is a screening measure, not a diagnosis: it tells you whether your weight is worth a closer look, not whether you are healthy.

How is BMI calculated?

For example, someone who is 170 cm (1.70 m) tall and weighs 68 kg has a BMI of 68 ÷ (1.70 × 1.70) = 68 ÷ 2.89 = 23.5.

This calculator accepts height in centimetres or in feet and inches, and weight in kilograms or pounds. It converts everything to metric before doing the maths, rounds the result to one decimal place, and reads your category from that rounded number.

BMI categories for adults

The World Health Organization's international ranges are used worldwide. For Asian populations, including Indians, the WHO Asia-Pacific guidance uses lower cut-offs for overweight and obesity, and Indian clinical guidelines follow the same thresholds.

This calculator shows your category on the WHO international scale, the one most BMI calculators use. If you are of South Asian origin, read your number against the Asian / Indian column too: from a BMI of 23.0, it is worth keeping an eye on your weight.

Why do Indians have lower BMI cut-offs?

At the same BMI, South Asian people tend to carry more body fat, and more of it around the abdomen, than people of European origin. A WHO expert consultation found that in many Asian populations the risk of type 2 diabetes and heart disease starts to climb at BMI levels between about 22 and 25, below the international overweight line of 25.

That is why a BMI of 24 can be normal on an international chart but overweight on an Asian one. If you are of South Asian origin, the Asian ranges give you an earlier and more useful signal.

What BMI does not tell you

• Muscle versus fat: BMI cannot tell them apart, so athletes and people who lift weights can show as overweight while being lean.
• Where fat sits: fat around the waist carries more risk than fat on the hips. For Indian adults, a waist above 90 cm in men or 80 cm in women is a common warning sign, whatever the BMI.
• Muscle loss with age: older adults naturally lose muscle, so a normal BMI can hide low muscle mass.
• Pregnancy: BMI is not meaningful during pregnancy. Doctors use your pre-pregnancy BMI to plan healthy weight gain.
• Children and teenagers: for ages 2 to 19, BMI has to be read against growth charts for age and sex, which this calculator does not do.

BMI and your health insurance

When you buy health or term insurance, insurers usually ask for your height and weight, and many use BMI as one input when they assess your application. A BMI well outside the healthy range can lead to a medical check-up before the policy is issued, a higher premium, or specific conditions on cover. The rules differ from insurer to insurer and plan to plan.

Always declare your height and weight accurately. A mismatch found at claim time can delay or affect the claim. If your BMI is high, it is still worth comparing plans, because insurers differ in how they treat it.

Moving towards a healthy BMI

• Aim for slow, steady change. Around half a kilo a week is realistic and easier to keep off.
• Build meals around vegetables, pulses, whole grains and protein, and cut back on sugary drinks, fried snacks and refined flour.
• Get at least 150 minutes of moderate activity a week, such as brisk walking or cycling, plus muscle-strengthening exercise on two days.
• Sleep seven to nine hours a night. Regular short sleep is linked to weight gain.
• If you are underweight, add energy- and protein-rich foods such as milk, curd, eggs, nuts and dals, and see a doctor to rule out an underlying cause.
• Talk to a doctor or registered dietitian before a big change, especially if you have diabetes, a thyroid condition or heart disease.

Frequently asked questions