Body Mass Index (BMI) is a simple screening measure that relates your weight to your height. It's quick to calculate and widely used by healthcare providers as a starting point — though, as explained below, it has real limitations and isn't a diagnosis on its own.
BMI Calculator
LiveHow BMI is calculated
BMI compares your weight to your height using one of two equivalent formulas, depending on the units you use.
A person is 170 cm tall and weighs 68 kg.
1.70² = 2.89
68 ÷ 2.89 = 23.5 — within the "normal weight" range.
BMI categories (WHO adult ranges)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Step-by-step guide
- Pick your unit system. Use Metric (cm/kg) or Imperial (ft, in, lb) — whichever matches how you measure at home.
- Enter your height and weight. The BMI figure and category update automatically.
- Read your category against the WHO ranges above.
- Talk to a healthcare provider for a full picture — BMI is a screening tool, not a diagnosis.
Limitations of BMI
BMI doesn't distinguish between muscle and fat, doesn't account for where fat is distributed, and uses the same thresholds regardless of age, sex, or ethnicity. A very muscular person can show a "high" BMI while having low body fat, and an older adult can have a "normal" BMI while having lost muscle mass. It's best used as one data point among several, not a stand-alone verdict on health.
Frequently asked questions
Is BMI accurate for athletes?
Not reliably. Because BMI can't tell muscle from fat, athletes and very muscular people often score in the "overweight" range despite having low body fat. Body composition measurements are more informative for this group.
Is this calculator suitable for children?
No. This tool uses the fixed adult BMI thresholds. Children and teens are assessed with age- and sex-specific growth charts, which a pediatrician can provide.
What should I do with my BMI result?
Treat it as a general screening number rather than a verdict. If you have questions about your weight or health, a doctor or registered dietitian can put your BMI in context alongside other factors.
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