How this calculation works
Use this BMI calculator to turn height and weight into body mass index (BMI). BMI is a simple screening measure for adults that can help you discuss weight-related health questions with a qualified clinician. It does not measure body composition, fitness, pregnancy status, or individual health risk, so treat it as a starting point rather than a diagnosis.
Mathematical formula and logic
BMI = weight in kilograms divided by height in meters squared.
Worked example
A person weighing 70 kg at 175 cm has a BMI of about 22.9.
What this calculator includes
- Metric BMI calculation
- Standard adult category reference
- Height and weight input validation
- Shareable calculation result
Understanding BMI
Body mass index is a ratio of weight to height. It is widely used as an inexpensive first screening tool because the formula can be repeated over time with the same two measurements. A single BMI result is best treated as a conversation starter: it may help you decide whether to review your lifestyle, monitor a trend, or speak with a clinician.
BMI does not measure body fat directly. It cannot distinguish muscle from fat, show where body fat is stored, or account for pregnancy, disability, or every medical condition. That is why a useful interpretation combines the result with symptoms, family history, waist measurement, physical activity, and professional advice where needed.
Standard adult BMI categories
The following standard adult categories are commonly used for screening. They are not diagnostic labels, and they are not designed for children or adolescents.
| BMI | Screening category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight range |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity range |
Why Indian and Asian BMI thresholds may differ
Clinical guidance from the World Health Organization (WHO) and the Ministry of Health and Family Welfare (India) adopts lower BMI cutoffs for South Asian populations because visceral adipose fat and cardiometabolic risks (type 2 diabetes, cardiovascular disease) emerge at lower body weights.
| Category | WHO Standard Threshold | Indian / Asian Threshold |
|---|---|---|
| Underweight | < 18.5 | < 18.5 |
| Normal / Healthy Weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25.0 – 29.9 | 23.0 – 27.4 |
| Obesity Class I | 30.0 – 34.9 | 27.5 – 32.4 |
| Obesity Class II | 35.0 – 39.9 | 32.5 – 37.4 |
| Obesity Class III (Severe) | ≥ 40.0 | ≥ 37.5 |
What to do after calculating your BMI
Record the result, then look for the trend rather than putting too much weight on one measurement. Use consistent scales, similar clothing, and a similar time of day when comparing results.
- Use the result as a screening prompt, not a diagnosis.
- Add waist measurement, activity, diet, sleep, and clinical markers to the wider picture.
- Avoid extreme changes in food intake or exercise without professional support.
- Speak with a qualified clinician for individual medical advice or if the result concerns you.
Calculation assumptions
- BMI is calculated for adults using metric units.
- The result is a screening estimate, not a medical diagnosis.
- Athletic build, pregnancy, age, and ethnicity can affect interpretation.
- Speak with a qualified clinician for personal medical advice.
Frequently asked questions
What does my BMI number mean?
For most adults, the standard World Health Organization screening categories are underweight below 18.5, healthy weight from 18.5 to 24.9, overweight from 25.0 to 29.9, and obesity from 30.0 upward. These bands describe a population-level screening measure, not a diagnosis. Your health history, waist measurement, blood pressure, activity level, and blood tests can all matter alongside BMI.
Is BMI an accurate measure of health?
BMI is useful because it relates weight to height in a simple, repeatable way, but it does not directly measure body fat or where fat is stored. A muscular athlete can have a high BMI without excess body fat, while someone with a BMI in the standard range can still have risk factors. Use BMI as one signal and discuss concerns with a qualified clinician.
What BMI range is healthy for Indian adults?
The standard adult screening range is 18.5 to 24.9. Some Indian and Asian clinical guidance uses lower action points, commonly around 23 for overweight and 25 for obesity, because health risks can appear at lower BMI levels in some Asian populations. There is no single personal target for everyone, so a clinician can interpret your BMI alongside waist size, medical history, and test results.
How is BMI calculated?
BMI equals weight in kilograms divided by height in metres squared: BMI = kg / m². For example, 70 kg divided by 1.75 m squared equals about 22.9. The calculator converts the height you enter in centimetres to metres before applying the formula. It is intended for adults and uses metric measurements to keep the calculation consistent.
What is the difference between BMI and body fat percentage?
BMI uses only height and weight, so it is a fast screening measure. Body fat percentage estimates how much of total body weight is fat, usually from skinfolds, circumference measurements, a smart scale, or clinical testing. Neither result is a complete health assessment. Comparing both can be more informative than relying on either one alone, especially when muscle mass is high.
My BMI shows overweight but I exercise regularly. Is this still a concern?
Regular exercise is valuable, and a higher BMI does not automatically mean poor health. Muscle mass, frame size, and measurement conditions can push BMI upward. Instead of reacting to one number, consider the trend over time, waist circumference, fitness, blood pressure, sleep, and clinician-led screening. A healthcare professional can help decide whether any follow-up is appropriate for you.
Can I use this BMI calculator for children?
No. Children and teenagers need age- and sex-specific BMI-for-age percentiles rather than the adult categories shown here. Growth patterns change quickly through childhood and adolescence, so the same adult BMI number can mean something different for a child. Use a paediatric growth chart or ask a paediatric clinician for an age-appropriate assessment.
How do I reduce my BMI safely?
Safe, sustainable changes usually focus on gradual habits rather than extreme diets: balanced meals, adequate protein and fibre, regular movement, resistance training where appropriate, sleep, and realistic portions. The right approach depends on medications, pregnancy, medical history, and eating patterns. Ask a doctor or registered dietitian for personalised guidance, especially if you have symptoms or a health condition.