BMI Calculator — Body Mass Index & Healthy Range
Free Body Mass Index calculator with metric and imperial units. See your BMI category and the healthy weight range for your height.
BMI categories (WHO)
| BMI range | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Normal |
| 25 – 29.9 | Overweight |
| ≥ 30 | Obese |
About this tool
Body Mass Indexis a simple ratio of weight to height squared, originally proposed by Adolphe Quetelet in the 1830s. It became the global default screening number because it's cheap (just a scale and a tape measure) and correlates reasonably with body-fat percentage at the population level. The WHO publishes the standard adult cutoffs used worldwide: 18.5, 25 and 30.
WRRK's BMI calculator runs the textbook formula in your browser, supports both metric and imperial, and computes the personalised healthy-weight range for your height — i.e. the kg and lb interval that maps to a "normal" BMI of 18.5–24.9. That range is far more actionable than the BMI number alone if you're setting a weight goal.
BMI has well-known limitations: it can't see body composition, so muscular athletes often read "overweight" and frail elderly people often read "normal" despite excess body fat. Use it as one of several inputs (waist-to-hip ratio, body-fat % via DEXA or callipers, blood pressure, lipid panel) rather than as a diagnosis.
How to calculate BMI (5 steps)
- Pick units. Metric (cm and kg) or Imperial (feet, inches, pounds). The toggle is at the top of the calculator.
- Enter height. Metric: a single value in centimetres. Imperial: feet and inches separately.
- Enter weight. In kilograms or pounds depending on unit choice.
- Read your BMI. Right panel shows the BMI value to one decimal and the WHO category (underweight, normal, overweight, obese).
- Use the healthy range. Below your BMI you'll see the kg and lb range that maps to a 'normal' BMI for your height — useful for setting weight goals.
Use cases
- Quick health screening at a check-up
- Setting a weight target — the healthy-range field shows your goal interval
- Tracking progress alongside body-fat measurements
- Filling out medical or insurance forms that ask for BMI
- Coaching clients in fitness or nutrition programmes
- Comparing populations in research or epidemiology
- Validating self-reported height/weight data
Frequently asked questions
+−What is BMI and how is it calculated?
BMI (Body Mass Index) is weight in kilograms divided by height in metres squared: BMI = kg ÷ m². For imperial units, multiply pounds by 703 and divide by inches squared. It's a quick screening number for whether your weight is in a healthy range for your height.
+−What BMI is considered healthy?
The World Health Organization defines: under 18.5 = underweight, 18.5 – 24.9 = normal weight, 25 – 29.9 = overweight, 30 or higher = obese. The 'normal' range is the same regardless of age or sex for adults.
+−Is BMI accurate for everyone?
BMI is a population-level screening tool, not a medical diagnosis. It doesn't distinguish muscle from fat, so very athletic people can read 'overweight' despite low body fat, and elderly people with muscle loss can read 'normal' despite high body fat. Use it alongside waist circumference, body-fat measurements, and a doctor's assessment.
+−How does BMI differ for Asian populations?
Health authorities in India, China and other Asian regions use lower thresholds because cardiometabolic risk rises at lower BMIs in these populations. A common Asian guideline: under 18.5 = underweight, 18.5 – 22.9 = normal, 23 – 24.9 = overweight, 25+ = obese. Check your local guideline.
+−What is the healthy weight range for my height?
Multiply 18.5 and 24.9 by your height in metres squared. For example, at 1.70 m: low = 18.5 × 1.70² ≈ 53.5 kg, high = 24.9 × 1.70² ≈ 72.0 kg. The calculator does this automatically and also shows the range in pounds.
+−Should children use this BMI calculator?
No — children and teens (under 20) need age-and-sex-specific BMI percentiles, not the adult cutoffs. Use a paediatric BMI-for-age chart instead (CDC or WHO growth references).
+−Does the calculator store my data?
No. All calculations run locally in your browser. Nothing is sent to a server, logged, or stored.