BMI Calculator
Enter your weight and height to instantly see your BMI, weight category, and a visual scale. Switch between metric and imperial units.
This is for general information only. Consult a healthcare professional for personalised advice.
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.
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
Get weekly tool tips & updates
New tools, power-user tips, and productivity hacks — delivered free every Friday.
No spam, ever. Unsubscribe with one click.
Why use BMI Calculator?
- Step-by-step explanations alongside every calculation
- Printable or shareable result summaries
- Works entirely offline in your browser
- Built-in input validation prevents common mistakes
Common use cases
- Calculate loan repayments before applying
- Check compound interest on savings accounts
- Estimate tax owed before filing
- Work out break-even point for a new business
- Plan retirement savings contributions
Related Calculators
TDEE Calculator
Calculate your Total Daily Energy Expenditure (TDEE) and get personalized calorie and macro targets for weight loss, maintenance, or muscle gain.
Body Fat Percentage Calculator
Calculate your body fat percentage using the US Navy or BMI method. Find your fat mass, lean mass, and fitness category. Free body fat estimator.
Ideal Weight Calculator
Calculate your ideal body weight using 4 proven formulas: Robinson, Miller, Devine, and Hamwi. Find the healthy weight range for your height.
Percentage Calculator
Calculate percentages instantly. Find what X% of a number is, what percentage X is of Y, or calculate percentage change.
Age Calculator
Calculate your exact age in years, months, and days. Find your next birthday countdown and day of birth. Free online age calculator.
Scientific Calculator
Free online scientific calculator with trigonometric functions, logarithms, powers, and constants. Supports keyboard input and calculation history.
Explore all Calculators.