How to use BMI Calculator
The BMI calculator computes your Body Mass Index from weight and height in metric (kg/cm) or imperial (lbs/ft/in). It classifies the result into one of four WHO categories — Underweight, Normal weight, Overweight and Obese — and displays a scale marker showing where your BMI falls. BMI is a quick population-level screening tool; it does not measure body fat directly.
- Select metric (kg/cm) or imperial (lbs/ft/in) units.
- Enter your weight and height.
- Your BMI and category update instantly on every keystroke.
- Expand the info section for healthy BMI weight ranges at your height.
Your data never leaves your device — 100% private processing.
BMI formula and WHO categories
Metric: BMI = weight (kg) ÷ height² (m²). Imperial: BMI = 703 × weight (lbs) ÷ height² (in²). WHO categories: Underweight < 18.5; Normal 18.5–24.9; Overweight 25–29.9; Obese ≥ 30. Class I Obesity is 30–34.9, Class II is 35–39.9, Class III (severe) is ≥ 40.
| Category | BMI range | Health risk |
|---|---|---|
| Underweight | < 18.5 | Nutritional deficiency, weakened immunity |
| Normal weight | 18.5–24.9 | Lowest risk for most adults |
| Overweight | 25–29.9 | Moderate risk for cardiometabolic disease |
| Obese (Class I) | 30–34.9 | High risk |
| Obese (Class II) | 35–39.9 | Very high risk |
| Obese (Class III) | ≥ 40 | Extremely high risk |
Limitations of BMI
BMI cannot distinguish between fat and muscle. A 90 kg athlete with 8% body fat will show "Overweight" or "Obese" despite excellent health. BMI also misclassifies risk in different ethnic groups: South and East Asian populations face elevated metabolic risk at BMI 23–25, below the standard "Overweight" threshold. For a more complete picture combine BMI with waist circumference (>102 cm in men or >88 cm in women indicates elevated abdominal fat risk) and other health markers.
Worked examples
Healthy-weight adult
Inputs: 70 kg · 1.75 m
Result: BMI 22.9 · Normal weight
Imperial input
Inputs: 180 lb · 5 ft 10 in
Result: BMI 25.8 · Overweight
Below the healthy range
Inputs: 50 kg · 1.70 m
Result: BMI 17.3 · Underweight
Healthy weight range by height (BMI 18.5–24.9)
| Height | Healthy weight range |
|---|---|
| 1.60 m (5’3″) | 47–64 kg (104–141 lb) |
| 1.70 m (5’7″) | 53–72 kg (118–159 lb) |
| 1.75 m (5’9″) | 57–76 kg (125–168 lb) |
| 1.80 m (5’11″) | 60–81 kg (132–178 lb) |
| 1.90 m (6’3″) | 67–90 kg (147–198 lb) |
Glossary
- BMI
- Body Mass Index — weight in kg divided by height in metres squared.
- WHO
- World Health Organization — defines international health standards including BMI categories.
- Adiposity
- The quality or state of being fat; excess adiposity is associated with metabolic disease.
- Waist circumference
- A measurement of abdominal fat; >102 cm in men or >88 cm in women indicates elevated metabolic risk.
Related reading
Frequently Asked Questions
Why use BMI Calculator?
- Computes BMI in both metric and imperial units with an instant live result
- Maps the result to a precise WHO category with clear health-risk context per band
- Displays a visual scale marker showing exactly where your BMI sits among all categories
- Shows the healthy weight range for your specific height so you know the target
Common use cases
- Screen body weight category before a GP appointment or annual health check
- Track BMI changes week by week as part of a structured diet or fitness programme
- Check whether a result meets an insurer's BMI eligibility threshold for coverage
- Compare your BMI against the adjusted cut-offs used for South and East Asian populations
- Calculate the weight needed to shift from one WHO category to the next
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