BMI Calculator
Body Mass Index · Metric & Imperial · Healthy weight range · Free · Instant · No signup
BMI Categories (WHO Classification)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of nutritional deficiency |
| 18.5 – 24.9 | Normal weight | Lowest risk of weight-related disease |
| 25.0 – 29.9 | Overweight | Increased risk of cardiovascular disease |
| 30.0 – 34.9 | Obese class I | High risk — weight loss recommended |
| 35.0 – 39.9 | Obese class II | Very high risk |
| 40.0 and above | Obese class III | Extremely high risk |
Frequently Asked Questions
How is BMI calculated?
BMI = weight (kg) ÷ height² (m²). For example, a person weighing 75 kg and 1.75 m tall has a BMI of 75 ÷ (1.75 × 1.75) = 24.5.
Is BMI accurate for everyone?
BMI is a simple screening tool, not a diagnostic measure. It can over-estimate body fat in people with a muscular build (e.g. athletes), and under-estimate it in older adults who have lost muscle mass. It also does not account for where fat is stored on the body, which affects health risk.
What is a healthy BMI?
The World Health Organization classifies a BMI of 18.5 to 24.9 as the healthy range for adults. However, optimal ranges may vary slightly by age, sex, and ethnicity.
Is this calculator private?
Yes. All calculations happen instantly in your browser using JavaScript. No data is sent to any server.
Can I use this for children?
No. BMI categories for children use age- and sex-specific percentile charts, which are different from adult classifications. This calculator is designed for adults aged 18 and over.
What if my BMI is outside the normal range?
If your BMI is outside the healthy range, speak to your GP or a registered dietitian. A healthcare professional can assess your individual situation and recommend a plan.