BMI Calculator
Free BMI calculator in metric or imperial units. See your body mass index, weight category and the healthy weight range for your height.
Your BMI
24.2
Healthy weight
Healthy weight for your height
53.5 kg – 72.0 kg
BMI is a screening measure, not a diagnosis — muscle mass, age and other factors matter. Consult a healthcare provider for personal advice.
Body Mass Index is weight divided by height squared. It was devised in the 1830s as a way of describing populations, and it remains the standard first-pass screening measure used by clinicians worldwide because it needs only two numbers anyone can measure.
This calculator gives your BMI in metric or imperial units, the WHO category it falls in, and the weight range considered healthy for your height. It is a screening indicator, not a diagnosis — the sections below explain where it works and where it misleads.
How to use the BMI Calculator
Choose metric or imperial
Metric takes centimetres and kilograms; imperial takes feet, inches and pounds.
Enter your height
Measure without shoes, standing straight against a wall, for the most accurate figure.
Enter your weight
Weighing at the same time of day, ideally in the morning, gives the most consistent tracking over time.
Read your BMI and category
The result shows your index, its WHO classification, and the healthy weight range for your height.
The formula
Metric: BMI = weight (kg) ÷ height (m)². Someone 1.75 m and 70 kg has a BMI of 70 ÷ 3.0625 = 22.9.
Imperial: BMI = 703 × weight (lb) ÷ height (in)². Someone 5′9″ (69 in) at 154 lb has 703 × 154 ÷ 4761 = 22.7.
WHO BMI categories for adults
| Category | BMI range | Notes |
|---|---|---|
| Underweight | Below 18.5 | May indicate undernutrition or an underlying condition |
| Healthy weight | 18.5 – 24.9 | Associated with the lowest average health risk |
| Overweight | 25.0 – 29.9 | Raised risk of cardiovascular and metabolic disease |
| Obesity class I | 30.0 – 34.9 | Moderate risk |
| Obesity class II | 35.0 – 39.9 | Severe risk |
| Obesity class III | 40.0 and above | Very severe risk |
These thresholds apply to adults aged 20 and over. Children and teenagers are assessed against age- and sex-specific percentile charts instead.
Where BMI is misleading
- Muscle weighs more than fat. A trained athlete can register as "obese" while carrying very little body fat. BMI measures mass, not composition.
- It ignores fat distribution. Visceral fat around the organs carries far more metabolic risk than fat on hips and thighs, and BMI cannot tell them apart.
- Ethnicity shifts the thresholds. Risk rises at lower BMI in South Asian, Chinese and Southeast Asian populations; many health bodies use 23 as the overweight threshold for these groups.
- Older adults lose muscle and height, which raises BMI without any gain in fat and can make a slightly higher BMI protective after 65.
- It is not validated in pregnancy or for people with significant fluid retention or limb loss.
Better measures to use alongside it
| Measure | What it captures | Healthy guide |
|---|---|---|
| Waist circumference | Abdominal fat directly | Under 40″ men, under 35″ women |
| Waist-to-height ratio | Central fat, scaled to frame | Keep waist under half your height |
| Waist-to-hip ratio | Fat distribution pattern | Under 0.90 men, under 0.85 women |
| Body fat percentage | Composition, not just mass | 8–19% men, 21–32% women |
Waist-to-height ratio is a strong and easily measured predictor of metabolic risk, and is now recommended alongside BMI by several national guidelines.
Using BMI sensibly
BMI is most useful as a trend for one person over time, and as a prompt for a fuller conversation rather than a verdict. A number that has drifted upward over three years says something worth acting on; a single reading three points from a threshold says very little.
If your BMI falls outside the healthy range, the next step is a clinician who can look at waist measurement, blood pressure, lipids and blood glucose together. Those markers, not the index, determine actual risk.
Frequently asked questions
What is a healthy BMI?
For most adults, 18.5 to 24.9. People of South Asian, Chinese or Southeast Asian descent face raised risk at lower values, and many guidelines use 23 as the overweight threshold for those groups.
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so a heavily trained person can be classified as overweight or obese despite very low body fat. Body fat percentage or waist measurement is more informative for athletes.
How do I calculate BMI manually?
Metric: weight in kilograms divided by height in metres squared. Imperial: 703 times weight in pounds, divided by height in inches squared.
Does BMI work for children?
Not with adult thresholds. Children and teenagers are plotted on age- and sex-specific percentile charts, because healthy body composition changes throughout growth.
What is a better measure than BMI?
Waist-to-height ratio is a strong, simple alternative — keeping your waist under half your height. Waist circumference and body fat percentage also capture risk that BMI misses.
Can I have a healthy BMI and still be unhealthy?
Yes. "Normal weight obesity" describes people within the healthy BMI range who carry high body fat and low muscle, and who show the metabolic markers associated with higher weight.
How quickly can I safely change my BMI?
Around 0.5–1 kg (1–2 lb) a week is the generally recommended rate of weight loss. Faster loss tends to shed muscle and water and is rarely sustained.
Is my health data stored?
No. Height and weight are used only in your browser to compute the result, and nothing is transmitted or saved.
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