How to Calculate BMI —
Step by Step Guide for Indians

The Formula

How to Calculate BMI — The Formula and Method

BMI is calculated by dividing your weight in kilograms by the square of your height in metres. For a person who weighs 70 kg and is 1.70 m tall: BMI = 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2. For Indians, this falls in the overweight category — not normal as Western charts suggest.

BMI stands for Body Mass Index. It is the most widely used health screening tool in the world precisely because it requires nothing more than your height and weight — measurements that anyone can take at home. Despite its simplicity, it provides a meaningful estimate of whether your body weight is appropriate for your height, and for Indians, it is most useful when interpreted with Indian-specific cutoffs rather than Western ones.

The formula was developed by Belgian mathematician Adolphe Quetelet in the 1830s and later adopted by the World Health Organization as a global screening standard. It is worth understanding that BMI was designed as a population screening tool — not as an individual diagnostic measure. This means your BMI number is a useful starting point for health assessment, not a definitive verdict on your health status. It works best when combined with other measurements like waist circumference and body fat percentage.

For Indians specifically, the importance of calculating BMI correctly — and then interpreting it with Indian cutoffs — cannot be overstated. India has over 101 million people with type 2 diabetes, and many developed the condition while their BMI appeared “normal” on Western charts. Using Indian cutoffs to interpret your BMI could be the difference between early intervention and a preventable chronic disease.

Step by Step

How to Calculate BMI Step by Step — With Worked Examples

Here is exactly how to calculate your BMI manually, with three worked examples at different heights and weights:

Step 1: Measure your weight in kilograms

Use a calibrated bathroom scale. Weigh yourself in the morning before eating or drinking, wearing minimal clothing. If your scale shows pounds, divide by 2.205 to convert to kilograms. If it shows stones, multiply by 6.35. Always use the same scale at the same time of day for consistency.

Step 2: Measure your height in metres

Stand straight against a wall without shoes. Mark the wall at the top of your head and measure the distance from floor to mark. Convert centimetres to metres by dividing by 100. For example: 165 cm ÷ 100 = 1.65 m. If you know your height in feet and inches, convert using: total inches × 0.0254 = metres.

Step 3: Square your height

Multiply your height in metres by itself. For example: 1.65 × 1.65 = 2.7225. This is your height squared (m²).

Step 4: Divide weight by height squared

Divide your weight (in kg) by your height squared (in m²). The result is your BMI. For example: 65 kg ÷ 2.7225 = 23.9.

Three worked examples

Imperial Method

How to Calculate BMI in Pounds and Inches (Imperial)

If you know your weight in pounds and height in feet and inches, use the imperial formula:

Step by step — imperial example

Person weighs 154 lbs and is 5 feet 6 inches tall (66 inches total):

1. Multiply weight by 703: 154 × 703 = 108,262
2. Square height in inches: 66 × 66 = 4,356
3. Divide: 108,262 ÷ 4,356 = 24.9 BMI
4. Interpret using Indian cutoffs: BMI 24.9 = Overweight for Indians (23–24.9)

Reading Your Result

How to Read Your BMI Result Using Indian Cutoffs

Once you have calculated your BMI, interpret it using Indian-specific categories — not Western ones:

The key difference from Western charts is that BMI 23–24.9 falls in the overweight category for Indians — not normal. Research published in The Lancet (2004) confirmed that South Asians develop metabolic complications at lower BMI values than Western populations, making these lower cutoffs medically essential for accurate risk assessment.

Limitations

Limitations of BMI — When the Calculation Is Not Enough

BMI is a useful starting point but has important limitations you must understand to use it correctly:

• It cannot distinguish muscle from fat. A person with high muscle mass may calculate a BMI in the overweight range despite having very low body fat. Athletes, bodybuilders, and people who do regular strength training often have BMIs above 23–25 that overestimate their actual health risk. Check body fat percentage alongside BMI for an accurate picture.
• It does not account for fat distribution. Where fat is stored matters as much as how much is stored. Visceral fat (around the organs) is far more dangerous than subcutaneous fat (under the skin). Two people with identical BMIs can have completely different fat distribution patterns and metabolic risk profiles. Waist circumference is a better indicator of visceral fat. Use the Waist-Hip Ratio Calculator to assess abdominal fat risk.
• It does not adjust for age. After age 30, adults lose muscle and gain fat even if weight stays the same. An older adult with a normal BMI may have significantly more body fat than a younger adult at the same BMI. For adults over 50, body fat percentage provides a more meaningful health assessment.
• It is the same formula for men and women. Women naturally carry 6–11% more body fat than men at the same BMI. A woman at BMI 22 has a higher body fat percentage than a man at the same BMI — but both are classified the same by the formula. Gender-specific interpretation of body fat percentage gives a more accurate picture.
• It ignores fitness level. Two people with identical BMI values — one sedentary, one physically active — have completely different cardiovascular fitness, insulin sensitivity, and long-term health outcomes. Fitness level is an independent predictor of health outcomes that BMI does not capture.

What to Do Next

What to Do After Calculating Your BMI

Knowing your BMI is the first step. Here is exactly what to do based on your result:

If your BMI is below 18.5 (Underweight)

Focus on increasing calorie intake with nutrient-dense foods. Use the Protein Calculator to ensure adequate protein for muscle building. Consult a doctor if weight loss is unintentional or rapid — this always warrants investigation.

If your BMI is 18.5–22.9 (Normal for Indians)

You are in the healthy range. Prioritise maintenance through balanced nutrition and regular activity. Even within normal BMI, check your waist circumference and consider using the Health Analyzer for a complete overview of your health metrics including body fat, TDEE, and ideal weight.

If your BMI is 23.0–24.9 (Overweight for Indians)

This is a metabolic risk zone. A 5% weight reduction — about 3–4 kg for a 70 kg person — produces significant improvements in blood sugar, blood pressure, and cholesterol. Use the TDEE Calculator to find your maintenance calories and the Weight Loss Calculator to set a 300–500 calorie daily deficit. Check your Diabetes Risk Score.

If your BMI is 25.0 and above (Obese for Indians)

Medical evaluation is strongly recommended alongside lifestyle changes. Get fasting blood glucose, HbA1c, blood pressure, and lipid profile checked. Talk to a DialFit expert — our volunteer dietitians create personalised plans at no cost, and can help you navigate an effective, sustainable approach to reaching a healthier BMI.

Common Questions

Frequently Asked Questions