BMI Calculator
Calculate your Body Mass Index and healthy weight range.
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This BMI calculator turns your weight in kilograms and height in centimetres into a Body Mass Index, labels it with the standard WHO category and shows the weight range that would keep your BMI between 18.5 and 24.9 at your height. It is meant for adults. Because health risks begin at a lower BMI in South Asians, this page also explains the tighter cut-offs used for Indians.
Entering your numbers
Type your weight into Weight (kg) and your height into Height (cm), then press Calculate BMI. Both fields take decimals. There is no feet, inches or pounds option, so convert first:
- Feet and inches to centimetres: total inches × 2.54. A height of 5 ft 6 in is 66 inches, or 167.64 cm.
- Pounds to kilograms: divide by 2.2046. So 154 lb is about 69.9 kg.
The height converter handles the first conversion if you prefer. For readings you can compare over time, weigh yourself at the same time of day, ideally in the morning before breakfast and in light clothing.
The result has three lines: Your BMI rounded to one decimal, the Category (Underweight, Normal weight, Overweight or Obese) and the Healthy weight range in kilograms for your height. The category is decided from the BMI as displayed, so a reading shown as 25 is labelled Overweight; 64 kg at 160 cm is one such case.
The formula, step by step
BMI = weight in kg ÷ (height in metres)². Take 70 kg at 170 cm:
- Height in metres: 170 ÷ 100 = 1.70.
- Square it: 1.70 × 1.70 = 2.89.
- Divide: 70 ÷ 2.89 = 24.22, displayed as 24.2 with the category Normal weight.
- Healthy range: 18.5 × 2.89 = 53.5 kg and 24.9 × 2.89 = 71.96 kg, shown as 72. The tool reports 53.5 – 72 kg.
The squaring also explains why a tall and a short person of equal weight get very different readings: height counts twice.
WHO categories and the Indian cut-offs
The labels the calculator prints follow the WHO adult classification. Studies in India have found that Asian Indians carry more body fat at a given BMI and develop diabetes and heart disease at lower BMI levels, so a 2009 consensus of Indian experts set lower thresholds. They are summarised in this review by Misra and Shrivastava:
| Category | WHO (used by the tool) | Asian Indian consensus |
|---|---|---|
| Underweight | Below 18.5 | Below 18.0 |
| Normal | 18.5 – 24.9 | 18.0 – 22.9 |
| Overweight | 25.0 – 29.9 | 23.0 – 24.9 |
| Obese | 30 and above | 25 and above |
Apply the Indian column to the worked example and 24.2 moves from normal to overweight. Staying at or below 22.9 at 170 cm would mean weighing about 66.2 kg or less (22.9 × 2.89). The same consensus treats a waist of 90 cm or more in men and 80 cm or more in women as abdominal obesity, a risk marker that BMI cannot see.
A revised definition published in 2025 by Misra and colleagues for the India Obesity Commission goes further and stops relying on BMI alone. It describes stage 1 obesity as a BMI above 23 without effects on organ function or daily activity. Stage 2 needs a BMI above 23 plus excess waist circumference or waist-to-height ratio, together with obesity-related symptoms or diseases.
Three more readings compared
| Weight, height | BMI shown | Tool's label | Indian scale |
|---|---|---|---|
| 58 kg, 160 cm | 22.7 | Normal weight | Normal |
| 72 kg, 168 cm | 25.5 | Overweight | Obese |
| 50 kg, 165 cm | 18.4 | Underweight | Normal |
The second row shows how much the choice of scale matters: the same person sits just over the WHO overweight line but inside the obese band on the Indian one. The third row works the other way, because the Indian scale starts its normal range at 18.0.
When BMI gives the wrong picture
- Muscular builds: people who lift weights or play contact sports can score "overweight" with little body fat. A body fat estimate or a waist measurement says more.
- Older adults: muscle lost with age can hide extra fat behind a normal-looking number.
- Children and teenagers: adult cut-offs do not apply. Their BMI is read against age- and sex-specific growth charts, so ask a paediatrician.
- Pregnancy: weight rises by design, so doctors judge weight gain against the BMI before pregnancy rather than a current reading.
Treat the result as a screening estimate, not a diagnosis or medical advice. If your reading falls in the Indian overweight or obese band, or your waist is above the cut-offs, a doctor can check blood sugar, blood pressure and cholesterol, which tell you far more than BMI does. One reading also says less than the trend, so recheck every month or two under the same conditions.