BMI Calculator
Enter your height and weight to instantly calculate your Body Mass Index, see your health category, and find your healthy weight range.
How to Use
- Choose your Unit System — Metric (centimetres / kilograms) or Imperial (inches / pounds).
- Enter your Height and Weight. Age and gender are optional and only used for reference notes, not for the BMI formula.
- Click Calculate BMI. Your BMI value, health category, and a visual scale marker appear instantly.
- Review the Healthy weight range and Weight difference to see how far you are from the normal range.
- Use Clear to reset all fields and start a new calculation.
BMI Categories (WHO Standard)
| Category | BMI Range (kg/m²) | Health Risk |
|---|---|---|
| Severe thinness | < 16.0 | High |
| Moderate thinness | 16.0 – 16.9 | Moderate |
| Mild thinness | 17.0 – 18.4 | Low |
| Normal range | 18.5 – 24.9 | Minimal |
| Overweight | 25.0 – 29.9 | Mildly increased |
| Obese Class I | 30.0 – 34.9 | Moderate |
| Obese Class II | 35.0 – 39.9 | High |
| Obese Class III | ≥ 40.0 | Very high |
Frequently Asked Questions
What is BMI and how is it calculated?
BMI (Body Mass Index) is a screening measure that uses your height and weight to estimate body fatness. The formula is BMI = weight(kg) / height(m)². In imperial units it is BMI = 703 × weight(lb) / height(in)². The result is a single number in kg/m².
Is BMI accurate for everyone?
BMI is a useful population-level screen, but it does not directly measure body fat or distribution. It may overestimate fatness for muscular athletes and underestimate it for older adults who have lost muscle mass. It is also not designed for children, pregnant women, or the elderly without further interpretation. Always consult a healthcare professional for individual assessment.
What is BMI Prime?
BMI Prime is the ratio of your BMI to the upper limit of the normal range (24.9). A value below 1.0 means you are under the normal ceiling, while a value above 1.0 means you are above it. It gives a quick sense of how far you sit from the normal-range boundary.
How is the healthy weight range calculated?
Using your height, the calculator finds the weight that corresponds to BMI 18.5 (lower bound) and BMI 24.9 (upper bound). The range is shown in your current unit system so you can use it as a long-term target zone.
Why do you ask for age and gender?
Age and gender are completely optional. They are not part of the standard BMI formula and do not change your result. They are only kept as context fields in case you want to record them for personal tracking, and they are never sent anywhere — all calculation happens locally in your browser.
What inputs are accepted and how are errors handled?
Height and weight accept positive numbers only. The calculator rejects empty fields, zero, negative values, and unrealistic ranges (for example, a height of 0 cm or a weight of 5000 kg). When an input is invalid, a toast notification explains the problem and the result area stays hidden until you correct it.
Is my data sent to a server?
No. Every calculation runs entirely in your browser. Nothing you type — height, weight, age, or gender — is ever transmitted to or stored on any server.
