BMI Calculator.
Enter your height and weight to get your Body Mass Index on a visual health scale.
Enter your height and weight above
to calculate your BMI.
What is Body Mass Index?
Body Mass Index is a widely used screening metric that relates a person's body weight to their height. Developed by Belgian mathematician Adolphe Quetelet in the 19th century, it provides a quick, costless way to categorise weight status across large populations. Doctors and public health agencies use it as the first filter when assessing weight-related health risks.
While BMI is a useful starting point, it has known limitations — it doesn't directly measure body fat percentage or account for muscle mass, bone density, age, sex, or ethnic differences in body composition. Always interpret BMI results in the context of a full health assessment.
BMI categories.
The World Health Organization ranges used to classify an adult BMI result.
| Category | BMI range | Associated risk |
|---|---|---|
| Underweight | < 18.5 | Malnutrition, weakened immunity, bone density loss |
| Normal weight | 18.5 – 24.9 | Lowest risk for weight-related health problems |
| Overweight | 25 – 29.9 | Elevated risk for hypertension, type 2 diabetes |
| Obese (Class I) | 30 – 34.9 | High risk for cardiovascular disease, sleep apnea |
| Obese (Class II) | 35 – 39.9 | Very high risk — consult a healthcare provider |
| Obese (Class III) | ≥ 40 | Extremely high risk — medical intervention recommended |
Capabilities
What You Get
A screening number you can actually read — both unit systems, the WHO category, and where you sit on the scale.
Metric And Imperial
Enter centimetres and kilograms or feet, inches, and pounds.
Instant Result
BMI recalculates as you type — no submit step in the way.
Visual Scale
See where your result sits across the full range, not just a bare number.
WHO Categories
Classified against the standard ranges health agencies actually use.
Healthy Weight Range
Shows the weight span that would place you in the healthy band.
Nothing Stored
Height and weight stay in the browser — no account, no logging.
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Random Number Generator
Generate one or many random numbers within a custom range. Options for integers or decimals, unique values only, and ascending/descending sort. Copy or download as a list.
FAQ
BMI Calculator FAQ.
What is BMI?
BMI (Body Mass Index) is a numerical value derived from a person's weight and height. It's calculated as weight (kg) divided by height (m) squared. It's used as a simple screening tool to categorise weight status, though it's not a diagnostic measure of body fatness or health.
What is a healthy BMI?
For adults, a BMI between 18.5 and 24.9 is considered normal or healthy. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese. These ranges are the same for both men and women.
Is BMI accurate?
BMI is a useful population-level screening tool, but it has limitations for individuals. It doesn't distinguish between fat mass and muscle mass — athletes may have a high BMI despite very low body fat. It also doesn't account for fat distribution, age, or ethnicity. Use it alongside other health indicators.
How is the BMI formula calculated?
For metric units: BMI = weight in kg ÷ (height in metres)². For imperial: BMI = (weight in pounds × 703) ÷ (height in inches)². Both formulas give the same result when properly converted.
Does BMI apply to children?
Children and teens use age- and sex-specific BMI percentiles rather than the adult categories. This tool is designed for adults aged 18 and over. For children, please consult a paediatric BMI chart.
What is the difference between overweight and obese?
Overweight (BMI 25–29.9) means you are above a healthy weight but below the obesity threshold. Obese (BMI 30+) indicates a higher level of excess weight that significantly increases health risks. Both categories benefit from lifestyle changes, but obesity typically warrants medical attention.
