BMI Calculator - Free Online BMI Tool

Unit System

Height

Weight

Your BMI

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What is a BMI?

A BMI calculator computes your Body Mass Index — a simple, widely recognised measure that relates your body weight to your height. The result is a single number used by doctors, fitness professionals, and public health organisations worldwide to screen for weight-related health conditions. Our free online BMI calculator supports both metric (cm, kg) and imperial (ft/in, lbs) inputs, making it convenient for users anywhere in India or abroad.

BMI was developed in the 19th century by Belgian statistician Adolphe Quetelet and has been adopted by the World Health Organisation as the global standard for classifying adult body weight. While it does not directly measure body fat, studies consistently show a strong correlation between BMI and metabolic risk factors such as type 2 diabetes, hypertension, dyslipidaemia, and cardiovascular disease — all conditions that are increasingly prevalent among Indian adults.

India faces a unique dual burden: a significant portion of the urban population is moving toward overweight and obesity, while rural undernutrition remains a serious concern. The National Family Health Survey (NFHS-5, 2019–21) found that 24% of Indian women and 23% of Indian men aged 15–49 are overweight or obese — a figure that has risen sharply over the past two decades. At the same time, 18% of women and 16% of men are still underweight. The BMI calculator helps individuals locate themselves within this spectrum and decide whether a lifestyle or medical intervention is warranted.

An important nuance for Indian users: research published in journals including The Lancet shows that South Asians accumulate visceral (abdominal) fat at lower BMI values than Caucasians, increasing metabolic risk even within the standard "Normal" range. The Indian Council of Medical Research (ICMR) therefore recommends treating a BMI of 23–24.9 as "Overweight" and ≥ 25 as "Obese" for Indian adults. Our calculator shows the global WHO categories, so if you are Indian and your BMI reads 23 or higher, treat it as a prompt for lifestyle review regardless of the label shown.

How to use this BMI calculator

Select your Unit System — choose Metric (cm, kg) if you know your measurements in centimetres and kilograms, or Imperial (ft, lbs) if you prefer feet, inches, and pounds. The calculator will convert automatically.
Enter your Height — in Metric mode, type your height in centimetres (e.g. 165). In Imperial mode, enter feet in the first box and inches in the second (e.g. 5 ft 5 in). Measure against a wall for accuracy; avoid measuring after a long day when height can decrease by up to 1 cm.
Enter your Weight — in Metric mode, enter your weight in kilograms; in Imperial mode, enter pounds. Use a calibrated digital scale and measure at the same time of day (morning, before eating, is recommended for consistency).
Read your BMI — the large number in the result card updates instantly. The colour-coded badge below it tells you your category (Underweight, Normal weight, Overweight, or Obese) and the BMI range that category covers.
Check your Healthy Weight Range — this shows the weight span (in your selected unit) that corresponds to a Normal BMI for your height. Use this as your goal window rather than fixating on a single target weight.
Interpret and act — if your BMI is in the Normal range, maintain your current habits. If you are Overweight or Obese, consult a doctor or registered dietitian before making significant dietary or exercise changes. If you are Underweight, a nutritional assessment is advisable to rule out deficiencies or underlying conditions.

Formula & Methodology

Metric formula:

BMI = weight (kg) ÷ height (m)²

Imperial formula:

BMI = 703 × weight (lbs) ÷ height (inches)²

Variable definitions:

- weight (kg) — body mass in kilograms
- height (m) — standing height in metres (centimetres divided by 100)
- weight (lbs) — body mass in pounds
- height (inches) — total height in inches (feet × 12 + remaining inches)

Healthy weight range:

- Min Healthy Weight (kg) = 18.5 × height (m)²
- Max Healthy Weight (kg) = 24.9 × height (m)²

Worked example — metric:

A person is 170 cm tall and weighs 72 kg.

1. Convert height: 170 ÷ 100 = 1.70 m
2. Square height: 1.70² = 2.89 m²
3. Compute BMI: 72 ÷ 2.89 = 24.9 — upper edge of Normal weight
4. Min healthy weight: 18.5 × 2.89 = 53.5 kg
5. Max healthy weight: 24.9 × 2.89 = 72.0 kg

Worked example — imperial:

A person is 5 ft 7 in tall and weighs 165 lbs.

1. Convert height to inches: (5 × 12) + 7 = 67 inches
2. Compute BMI: 703 × 165 ÷ 67² = 115,995 ÷ 4,489 = 25.8 — Overweight
3. The calculator internally converts 165 lbs to 74.8 kg and 67 inches to 170.2 cm before applying the metric formula, giving the same result.

Assumptions and limitations:

- The calculator uses standard WHO cut-off points (18.5 / 25 / 30). It does not apply ICMR or Asia-Pacific revised thresholds automatically — Indian users should mentally shift the Overweight boundary to 23.
- BMI does not account for muscle mass, bone density, age-related muscle loss (sarcopenia), or fat distribution. Waist circumference and body fat percentage provide complementary information.
- Results are rounded to one decimal place. No rounding errors are introduced by the calculator — only the displayed output is rounded, not intermediate values.

Frequently Asked Questions

What is BMI and how is it calculated?

BMI, or Body Mass Index, is a numerical value derived from a person's weight and height. It is calculated by dividing your weight in kilograms by the square of your height in metres (kg/m²). For example, a person weighing 70 kg at 170 cm has a BMI of 24.2. It is a widely used screening tool to categorise body weight relative to height.

What are the BMI categories for adults?

The standard WHO BMI categories for adults are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (30 and above). These categories apply to both men and women aged 18 and over. Children and teenagers use age- and sex-specific BMI percentiles rather than these fixed ranges.

Is the BMI scale different for Indians?

Yes. Research shows that people of South Asian origin, including Indians, carry a higher proportion of body fat at a lower BMI compared to Caucasian populations. The Indian Council of Medical Research (ICMR) and several Asian health bodies recommend lower cut-off points: Overweight at BMI ≥ 23 and Obese at BMI ≥ 25. Our calculator displays standard WHO categories, so Indian users should treat a BMI between 23 and 24.9 as a warning zone even if it falls in the 'Normal' band.

What is the formula for BMI?

The metric formula is BMI = weight (kg) ÷ height (m)². For imperial measurements, the formula is BMI = 703 × weight (lbs) ÷ height (inches)². Both formulas produce the same result — our BMI calculator automatically converts imperial inputs to metric before applying the standard formula.

What is a healthy BMI for Indian adults?

Using the standard WHO scale, a BMI between 18.5 and 24.9 is considered healthy. However, given the ICMR's revised guidelines for South Asians, Indian adults should ideally aim for a BMI between 18.5 and 22.9 for the lowest metabolic risk. The healthy weight range shown by our BMI calculator is based on the standard 18.5–24.9 band applied to your specific height.

Can BMI be used for children and teenagers?

BMI can be calculated for children and teenagers, but it is interpreted differently. Instead of fixed cut-offs, BMI is plotted on age- and sex-specific growth charts as a percentile. A child is considered overweight if their BMI is at or above the 85th percentile and obese at or above the 95th percentile for their age and sex. The BMI calculator on this page is designed for adults aged 18 and above.

How do I convert my height from feet and inches to centimetres for the BMI calculator?

You do not need to convert manually — our BMI calculator includes an Imperial mode where you can enter your height in feet and inches directly. If you prefer to convert: 1 foot equals 30.48 cm and 1 inch equals 2.54 cm. For example, 5 feet 7 inches equals (5 × 30.48) + (7 × 2.54) = 152.4 + 17.78 = 170.18 cm.

What is the difference between BMI and body fat percentage?

BMI is a ratio of weight to height and is a proxy for body fatness, not a direct measurement. Body fat percentage measures the actual proportion of fat mass in your body relative to total body weight. Two people with the same BMI can have very different body fat percentages — for instance, a muscular athlete may have a high BMI but low body fat. For a more accurate health assessment, BMI should be used alongside waist circumference and, where possible, a DEXA scan or bioelectrical impedance test.

How often should I check my BMI?

For most healthy adults, checking BMI every 3–6 months is sufficient to track body weight trends. If you are actively trying to lose or gain weight, checking monthly gives a clearer picture of progress. Use our [Percentage Change Calculator](/percentage-change-calculator/) alongside your BMI check to quantify how much your weight has changed in percentage terms since your last measurement.

Does BMI apply the same way to men and women?

The BMI formula and cut-off categories are the same for men and women, but women naturally carry a higher percentage of body fat at any given BMI due to physiological differences. A BMI of 22 in a woman may represent a higher absolute fat mass than the same BMI in a man. This limitation is one reason health professionals also consider waist-to-hip ratio and body composition when assessing health risk.

What should I do if my BMI is outside the healthy range?

If your BMI is below 18.5, consult a doctor or registered dietitian to rule out nutritional deficiencies. If your BMI is in the overweight or obese range, a combination of a calorie-controlled diet and regular physical activity (at least 150 minutes of moderate exercise per week, per WHO guidelines) is the recommended first step. Always consult a healthcare professional before starting any significant diet or exercise programme, particularly if you have pre-existing conditions.

Is BMI alone enough to assess my health risk?

No. BMI is a useful population-level screening tool, but it has well-known limitations at the individual level. It does not distinguish between muscle and fat, does not account for fat distribution, and may misclassify older adults who have lost muscle mass. Waist circumference (risk increases above 80 cm for women and 90 cm for men by Indian standards), blood pressure, fasting glucose, and lipid profiles together give a much more complete health picture than BMI alone.