⚖️ BMI & Body Fat Calculator

How to Calculate Your BMI

1. Choose metric or imperial units.
2. Enter your weight and height.
3. Add your age and sex to get the body fat estimate as well.
4. Read your BMI, which category it falls into, and your healthy weight range.
5. Check the table to see where your number sits against the WHO thresholds.

What is BMI and how is it calculated?

Body Mass Index is your weight in kilograms divided by the square of your height in metres. A person weighing 70 kg at 1.75 m has a BMI of 70 divided by 3.06, which is 22.9. It was designed in the 19th century as a way to describe populations, and it remains useful because it needs only two measurements that anyone can take at home.

What are the limitations of BMI?

It cannot tell muscle from fat. A muscular athlete can register as "overweight" while carrying very little body fat, and someone with low muscle mass can sit in the healthy range while carrying too much. It also ignores where fat is stored, which matters — fat around the abdomen carries more health risk than fat on the hips. Waist circumference and waist-to-height ratio capture that better, and are worth measuring alongside BMI.

Do the categories apply to everyone?

No. The standard thresholds were derived largely from European populations. Several health bodies recommend lower cut-offs for people of South Asian, Chinese and other Asian descent, where cardiovascular and diabetes risk rises at a lower BMI — often using 23 rather than 25 as the overweight threshold. BMI is also interpreted differently for children and teenagers, who are assessed against age and sex percentile charts instead, and it is not a valid measure during pregnancy.

How accurate is the body fat estimate?

It is an approximation. The figure here uses the Deurenberg equation, which predicts body fat from BMI, age and sex. It is reasonably good across large groups but can be off by several percentage points for any individual, particularly for very fit or very sedentary people. For a real measurement you would need a DEXA scan, hydrostatic weighing or at minimum calliper testing by someone trained to do it.

Is this medical advice?

No. This calculator provides general information only. BMI is a screening tool that flags whether a conversation is worth having, not a diagnosis. If you are concerned about your weight or health, speak to a doctor who can consider your full history, body composition, blood work and lifestyle.