BMI Calculator
Calculate your Body Mass Index from height and weight in metric or imperial units. See your BMI category, healthy weight range and how far you are from it.
How BMI works
Body Mass Index estimates whether your weight is proportionate to your height. It is used worldwide as a quick
screening measure for weight-related health risk:
BMI = weight (kg) ÷ height (m)²
Adult BMI categories (WHO)
| BMI | Category |
|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Worked example
Someone who is 5′7″ (170 cm) and 70 kg (154 lb): height in metres is 1.70, squared is 2.89,
and 70 ÷ 2.89 = BMI 24.2 — inside the healthy range, whose weight span for that height is
about 53.5 to 72 kg.
Limitations worth knowing
BMI can misclassify muscular builds as overweight and does not capture where fat is carried — abdominal fat carries
higher risk. It is best read together with waist circumference or a body-fat percentage estimate.
Frequently asked questions
What is a healthy BMI?
For adults, the World Health Organization defines a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classed as obese.
How is BMI calculated?
BMI = weight in kilograms ÷ (height in metres)². For example, 70 kg at 1.75 m gives 70 ÷ 3.0625 = 22.9. Imperial inputs are converted to metric before applying the same formula.
Is BMI accurate for everyone?
BMI is a screening tool, not a diagnosis. It does not distinguish muscle from fat, so very muscular people can read "overweight", and it applies differently to children, pregnant women and the elderly. Pair it with waist measurements or a body-fat estimate for a fuller picture.
Does BMI differ for men and women?
The standard adult BMI categories are the same for men and women. Body composition differs by sex, which is one of BMI’s limitations — our Body Fat Calculator accounts for sex explicitly.
What should I do if my BMI is outside the healthy range?
The result shows the weight range that corresponds to a healthy BMI for your height, so you can see how far you are from it. For any decisions about diet or training, talk to a doctor or registered dietitian.
This tool provides general health information, not medical advice. Consult a healthcare professional before making decisions based on it.