BMI Calculator — Free Body Mass Index Calculator

Calculate your BMI in metric or imperial units and see the healthy weight range for your height.

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Your BMI
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BMI is a population screening tool, not a diagnosis. It uses only height and weight, so it cannot tell muscle from fat — very muscular people often read as “overweight” while someone at a healthy weight may still carry excess body fat. It is also less reliable for children, pregnant women, older adults, and across some ethnic groups, where different thresholds apply. Talk to a doctor before acting on any number here.

Enter your height and weight in metric or imperial units to get your Body Mass Index, the category it falls in, and the weight range considered healthy for your height.

How to use BMI Calculator

  1. Choose metric or imperial units.
  2. Enter your height and weight.
  3. Read your BMI and where it sits on the scale.

How BMI is calculated

BMI is your weight in kilograms divided by your height in metres squared. The imperial version multiplies pounds by 703 and divides by height in inches squared — the same formula with unit conversion folded into a constant.

The standard categories

Under 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight, and 30 or above is obese. These thresholds come from World Health Organization guidance for adults.

What BMI cannot tell you

BMI uses only height and weight, so it has no way to distinguish muscle from fat or to know where fat is carried. A muscular athlete frequently reads as "overweight" or even "obese" while being in excellent health. Conversely someone within the healthy range can carry a high proportion of body fat with low muscle mass.

It is also less reliable for children and teenagers (who need age and sex-specific percentile charts), pregnant women, older adults who have lost muscle, and across some ethnic groups — health authorities in several countries apply lower thresholds for people of South Asian descent, for whom risk rises at a lower BMI.

BMI was designed in the 1830s to describe populations, not to diagnose individuals. It remains a useful, cheap screening signal at population scale. As a personal health verdict it is a starting point for a conversation with a doctor, not an answer. Waist circumference, body-fat percentage, blood pressure and blood markers all tell you more.

Frequently asked questions

Is BMI accurate for everyone?

No. It uses only height and weight, so it cannot distinguish muscle from fat. Athletes often read as overweight while being very healthy. It is also less reliable for children, pregnant women, older adults and across some ethnic groups.

What is a healthy BMI?

18.5 to 24.9 for adults under WHO guidance. Several countries apply lower thresholds for people of South Asian descent, where health risks rise at a lower BMI.

What measures health better than BMI?

Waist circumference, waist-to-height ratio, body-fat percentage, blood pressure and blood markers all tell you more about an individual. BMI is a population screening tool, not a diagnosis.

Can I use this for my child?

Not reliably. Children and teenagers need age and sex-specific percentile charts rather than the adult thresholds. Ask a paediatrician.

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