Free BMI Calculator: check your Body Mass Index in metric or imperial units, see your weight category, healthy weight range, and ideal weight instantly. Wondering if your weight is in a healthy range for your height? Our free BMI Calculator gives you your Body Mass Index in seconds. Enter your height and weight in metric (kg/cm) or imperial (lb/ft/in) units to see your BMI score, weight category, healthy weight range for your height, and how much you would need to gain or lose to reach a healthy BMI. It also includes an adult BMI gauge, BMI Prime, ponderal index, an estimated ideal weight, and a child and teen mode for ages 2 to 19. Everything is calculated instantly in your browser, and your data is never stored or sent anywhere.
- Healthy weight range
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- To reach a healthy BMI
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- BMI Prime
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- Ponderal Index
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- Ideal weight (Devine)
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BMI Categories (WHO, adults)
| Category | BMI Range |
|---|---|
| Severe thinness | < 16 |
| Moderate thinness | 16 – 16.9 |
| Mild thinness | 17 – 18.4 |
| Normal (healthy) | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese Class I | 30 – 34.9 |
| Obese Class II | 35 – 39.9 |
| Obese Class III | ≥ 40 |
BMI is a screening tool, not a diagnosis. It does not measure body fat directly and may be less accurate for athletes, older adults and pregnant women. Consult a healthcare professional for personal advice.
How to Use the BMI Calculator
- Choose your unit system: Metric (kg, cm) or Imperial (lb, ft, in).
- Select Adult (20+) or Child/Teen (2–19), and enter your age and gender if asked.
- Enter your height and your weight.
- Click Calculate BMI, or just type and the result updates live.
- Read your BMI score, category, healthy weight range and the gauge marker.
- Use the “Weight to gain/lose” line to see how far you are from the healthy range.
- Click Reset to start over.
FAQs
- What is BMI? BMI (Body Mass Index) is a number calculated from your weight and height: BMI = weight (kg) ÷ height (m)². It is a screening tool for weight categories.
- What is a healthy BMI range? For adults, the WHO 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 obese.
- Is BMI accurate for everyone? No. BMI doesn’t distinguish muscle from fat, so athletes and very muscular people may score high, and it may be less accurate for older adults and some ethnic groups. Use it as a starting point, not a diagnosis.
- How is BMI different for children and teens? For ages 2 to 19, BMI is compared with children of the same age and sex using percentiles, not fixed cut-offs. This tool shows an approximate category for that age group.
- What is BMI Prime? BMI Prime is your BMI divided by 25 (the upper limit of the healthy range). A value below 1.0 is under the overweight threshold.
- Should I see a doctor? If your result is outside the healthy range, or you have health concerns, talk to a doctor or dietitian. This calculator is informational only and not medical advice.
What it includes:
- Units: you can switch between metric and imperial, and your entries convert when you switch.
- Modes: Adult (20+) uses WHO categories and shows a colour gauge with a marker. Child/Teen (2–19) uses age- and gender-based percentile cut-offs.
- Results: BMI score and category, healthy weight range, how much to gain or lose to reach it, and advice text.
- Adult extras: BMI Prime, ponderal index, and ideal weight (Devine formula).
- Reference: a WHO category table below the calculator that highlights your category.
- Setup: results update live as you type, entries are validated, and nothing is stored or sent anywhere.
