BMI Calculator

What is BMI and How is it Calculated?

Body Mass Index (BMI) is a simple measure that uses height and weight to indicate whether an adult falls within an underweight, healthy weight, overweight or obesity range. The Graphic Era Hospital BMI Calculator provides a quick way to calculate BMI and understand how weight compares with height.

While BMI is useful as an initial screening measure, it does not directly measure body fat or provide a complete picture of overall health. Therefore, the result should be viewed as a general guide rather than a diagnosis. If the result falls outside the healthy range or there are concerns about weight or related health risks, a doctor or dietitian can provide a more detailed assessment.

BMI Calculation Formula

BMI is calculated by dividing weight in kilograms by the square of height in metres:

BMI = Weight (kg) ÷ Height² (m²)

For example, for an adult who weighs 70 kg and is 1.75 metres tall:

BMI = 70 ÷ (1.75 × 1.75) = 22.9

The resulting number can then be compared with the appropriate adult BMI ranges to understand the corresponding weight category.

Understanding Your BMI Result

Once BMI is calculated, it can be compared with BMI cut-offs recommended for Asian Indian adults. These cut-offs are lower than standard international ranges because weight-related health risks, such as diabetes and cardiovascular disease, can develop at a lower BMI in Asian populations.

BMI Chart and Categories for Adults

What Does Each BMI Category Mean?

Underweight: BMI Below 18.5

A BMI below 18.5 falls within the underweight range. Being underweight can have different causes, so persistent low weight, unexplained weight loss or difficulty gaining weight may require medical or nutritional assessment.

Healthy Weight: BMI 18.5-22.9

A BMI between 18.5 and 22.9 falls within the healthy weight range under the Asia-Pacific cut-offs used by this calculator. However, BMI alone does not provide a complete picture of health. Blood pressure, cholesterol, blood sugar, waist circumference, lifestyle and other health factors may also be considered during an assessment.

Overweight: BMI 23.0-24.9

A BMI between 23.0 and 24.9 falls within the overweight range for Asian Indian adults. The result can be considered alongside factors such as waist circumference, physical activity, eating habits and existing health conditions to better understand weight-related health risks.

Obesity Class I: BMI 25.0-29.9

A BMI between 25.0 and 29.9 falls within Obesity Class I under the Asia-Pacific classification used by this calculator. A medical assessment can help evaluate other risk factors and determine whether changes in nutrition, physical activity or other forms of weight-management support may be appropriate.

Obesity Class II: BMI 30.0 and Above

A BMI of 30.0 or above falls within Obesity Class II. Higher BMI may be associated with an increased risk of several chronic health conditions, although BMI alone does not determine an individual's overall health risk. A doctor can assess BMI alongside other clinical and lifestyle factors and recommend appropriate weight-management support where required.

Is BMI an Accurate Measure of Healthy Weight?

BMI is a useful screening measure, but it does not provide a complete assessment of an individual's health. It estimates weight in relation to height and can help identify whether an adult falls within an underweight, healthy weight, overweight or obesity range. However, BMI does not directly measure body fat or distinguish fat from muscle and bone.

For example, a person with high muscle mass may have a higher BMI without having excess body fat. BMI also does not show where fat is stored in the body, which can be relevant when assessing health risks.

For a more complete assessment, a doctor may consider BMI alongside other factors, such as:

• Waist circumference
• Blood pressure
• Blood sugar and cholesterol levels
• Medical and family history
• Physical activity and eating habits
• Overall body composition and physical examination

Therefore, a BMI result is best viewed as a starting point. A doctor or dietitian can interpret it in the context of other health indicators when weight or associated health risks are a concern.

Does BMI Differ for Men and Women?

For adults, BMI is calculated in the same way for men and women using height and weight. The Asia-Pacific adult BMI cut-offs used by this calculator also do not use separate categories based on sex.

However, the same BMI does not necessarily indicate the same body composition. At a given BMI, the proportion and distribution of body fat can differ between men and women. BMI also cannot distinguish body fat from muscle or show where fat is stored in the body.

For this reason, BMI should be considered alongside other health indicators when a more detailed assessment is needed. A doctor may also evaluate factors such as waist circumference, body composition, blood pressure, blood sugar, cholesterol levels and medical history to understand weight-related health risks more accurately.

How is BMI Assessed in Children and Teenagers?

BMI in children and teenagers is interpreted differently from adult BMI because body composition changes as children grow. Although BMI is still calculated using height and weight, the result is assessed in relation to the child's age and sex rather than compared directly with adult BMI cut-offs.

For children and adolescents, BMI is generally plotted on an age- and sex-specific growth chart or compared with BMI-for-age reference values. This helps assess how a child's BMI compares with expected growth patterns for others of the same age and sex.

Adult BMI categories should therefore not be applied directly to children or teenagers. Growth charts are also not intended to diagnose a health condition on their own. A paediatrician may consider the child's growth pattern over time, stage of development, medical history, diet and activity levels before deciding whether further assessment is needed.

When Should You Consult a Doctor About BMI?

A BMI outside the healthy range does not necessarily mean there is a health problem, but it can be a reason to look more closely at weight, nutrition and other health indicators. Medical advice may be helpful when BMI changes significantly, remains outside the recommended range or occurs alongside other health concerns.

Consider consulting a doctor or dietitian if there is:

• Persistent underweight, overweight or obesity, particularly when there are concerns about nutrition or overall health.
• Unexplained or sudden weight loss, especially without changes in diet or physical activity.
• Difficulty gaining or losing weight despite appropriate dietary and lifestyle changes.
• Overweight or obesity alongside conditions such as diabetes, high blood pressure, high cholesterol, joint problems or sleep apnoea.
• Concern about a child or teenager's growth or weight, as BMI in this age group needs to be assessed using age- and sex-specific growth references.
• A medical condition or medicine that may be affecting body weight.
• A need for personalised guidance on diet, nutrition or healthy weight management.

At Graphic Era Hospital, our Nutrition & Dietetics team help individuals understand their nutritional needs, make practical dietary changes and work towards a healthier weight with guidance suited to their health and lifestyle. If weight concerns are linked to conditions such as obesity, diabetes or other metabolic problems, care may also involve the Diabetes & Endocrinology team for further evaluation and management.