BMI Calculator
Calculate your Body Mass Index instantly from metric or imperial inputs — WHO categories, visual range bar, fully private, runs in-browser.
Enter your weight and height above to calculate your BMI.
Understanding Your BMI
Body Mass Index is one of the most widely used health screening tools in the world. Developed by the Belgian mathematician Adolphe Quetelet in the 1830s and later adopted by the World Health Organization, BMI provides a single number that gives clinicians a quick, equipment-free snapshot of whether a person's weight is proportionate to their height. Despite being over a century old, it remains the standard first-pass metric in clinical guidelines, insurance assessments, and population health surveys.
How BMI Is Calculated
The formula is straightforward: divide your weight in kilograms by your height in metres squared. A person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. If you think in pounds and feet, this calculator handles the unit conversion for you automatically — just switch to Imperial mode, enter your weight in pounds and your height in feet and inches, and the same result appears instantly.
WHO Classification Ranges
- Underweight — below 18.5: May indicate malnutrition, an eating disorder, or other underlying conditions. Can affect bone density, immune function, and energy levels.
- Normal weight — 18.5 to 24.9: Associated with the lowest risk of weight-related diseases for most adults according to large-scale epidemiological data.
- Overweight — 25 to 29.9: Elevated risk for type 2 diabetes, cardiovascular disease, and joint problems. Modest lifestyle changes often produce measurable improvements.
- Obese — 30 and above: Substantially increased risk across multiple chronic conditions. The WHO further divides obesity into Class I (30–34.9), Class II (35–39.9), and Class III (≥ 40).
Limitations to Keep in Mind
BMI's biggest weakness is that it treats weight as a proxy for fat, which it isn't. A professional rugby player and a sedentary office worker might share the same BMI while having completely different body compositions. Older adults tend to carry more visceral fat at a given BMI than younger adults do, and research consistently shows the thresholds may be too lenient for people of South Asian, East Asian, and some other ethnic backgrounds, where health risks emerge at lower BMI values.
Complementary measures — waist circumference, waist-to-hip ratio, body fat percentage via DXA or skinfold calipers, and blood-panel markers — give a fuller picture. Your healthcare provider can interpret these together to give personalised guidance that a single number cannot.
Privacy
This BMI calculator runs entirely in your browser. Your weight, height, and results never leave your device — there are no network requests and nothing is logged or stored anywhere. You can use it with complete confidence.
Frequently Asked Questions
What is BMI and what does the number mean?↓
BMI (Body Mass Index) is a simple ratio of weight to height squared — kilograms divided by metres squared. The World Health Organization uses four ranges: below 18.5 is Underweight, 18.5–24.9 is Normal weight, 25–29.9 is Overweight, and 30 or above is Obese. It's a quick population-level screening metric, not a clinical diagnosis. Two people with the same BMI can have very different body compositions.
How do I calculate BMI in imperial units (pounds and inches)?↓
Switch the tool to Imperial mode, enter your weight in pounds and your height in feet and inches. The calculator converts them internally — pounds to kilograms (÷ 2.20462) and total inches to centimetres (× 2.54) — then applies the standard BMI formula. The result is the same as the metric calculation.
Is BMI accurate for everyone?↓
BMI has well-known limitations. It doesn't distinguish muscle from fat, so athletes and bodybuilders often score in the Overweight range despite having very low body fat. It also doesn't account for age, sex, or ethnicity. Older adults typically carry more fat at the same BMI than younger adults, and studies show the Obese threshold may need adjustment for certain ethnic groups. Think of BMI as a starting point, not a final verdict.
What BMI is considered healthy?↓
The WHO defines the healthy (Normal) BMI range as 18.5 to 24.9 for adults. Below 18.5 suggests insufficient body weight; 25–29.9 indicates Overweight; 30 or above indicates Obesity. These thresholds were established from large epidemiological studies linking BMI to disease risk.
Does this tool store or send my data anywhere?↓
No. All calculations happen locally in your browser using JavaScript. No data — weight, height, or results — is transmitted to any server or stored anywhere outside your device.