BMI Calculator
Check your Body Mass Index instantly — free, metric & imperial, no signup needed
< 18.5
18.5 – 24.9
25 – 29.9
≥ 30
What is this BMI Calculator?
This free BMI calculator computes your Body Mass Index instantly from your height and weight, then classifies the result using WHO (World Health Organization) standards into one of four categories: Underweight, Normal weight, Overweight, or Obese. The result is colour-coded and highlighted on a visual scale so you can see at a glance where your BMI falls. It supports both metric units (kg and cm) and imperial units (lbs, feet and inches) — switch between them with the tab at the top of the calculator.
Unlike many BMI tools that just show a number, this calculator provides a plain-language interpretation of what your result means for your health, and highlights the relevant segment on the BMI scale bar. For Indian and South Asian users, the article below also explains the lower BMI thresholds recommended for Asians — because the standard WHO cutoffs (25 for overweight, 30 for obese) are known to underestimate health risks in South Asian populations.
How to use this calculator
- Step 1 — Choose your unit system: Click "Metric (kg, cm)" if you know your height in centimetres and weight in kilograms — this is the default and most common in India. Click "Imperial (lbs, in)" if you know your measurements in pounds, feet, and inches (common in the US).
- Step 2 — Enter your height: Metric: enter height in centimetres (e.g. 165 cm). Imperial: enter feet (e.g. 5) and inches (e.g. 5) separately. Do not include shoes — measure in bare feet for accuracy.
- Step 3 — Enter your weight: Metric: kilograms (e.g. 68 kg). Imperial: pounds (e.g. 150 lbs). Weigh yourself in the morning before eating for the most consistent reading.
- Step 4 — Click Calculate BMI: Or press Enter. Your BMI appears as a large number, colour-coded by category. The scale bar below highlights which zone your BMI falls in — blue (underweight), green (normal), orange (overweight), or red (obese).
- Step 5 — Read the interpretation: Below the category pill, a plain-language message explains what your result means and what action, if any, is worth considering.
- Step 6 — Copy your result: Click "Copy Results" to copy your BMI and category to your clipboard — useful for sharing with a doctor or logging in a health app.
Key features
- WHO BMI classification: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese (≥30) with obesity sub-classes
- Metric and imperial: Switch instantly between kg/cm and lbs/ft+in — no manual conversion needed
- Visual scale bar: Active segment highlights your exact category with a coloured outline
- Colour-coded result: Blue, green, orange, and red match the category — immediately readable
- Copy results: One-click copy of your BMI and category for sharing or record-keeping
- Auto-calculates on load: Shows a result immediately with default values so new users understand the tool at a glance
Understanding BMI — what your number means, its limitations, and what to do next
BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s as a statistical tool for studying populations — not as a medical diagnostic for individuals. Despite this, it became the world's most widely used weight-screening tool because it requires only two measurements anyone can take at home: height and weight. Understanding what it can and cannot tell you is essential to using it correctly.
The BMI formula — how it is calculated
Metric formula: BMI = weight (kg) ÷ height² (m²). Example: a person who is 170 cm tall and weighs 70 kg → BMI = 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2 (Normal weight).
Imperial formula: BMI = [weight (lbs) ÷ height² (inches²)] × 703. Example: a person who is 5 ft 7 in (67 inches) and weighs 154 lbs → BMI = (154 ÷ 67²) × 703 = (154 ÷ 4489) × 703 = 0.0343 × 703 = 24.1 (Normal weight). This calculator performs both computations automatically — you never need to do the maths.
WHO BMI categories — complete classification with health implications
Underweight — BMI below 18.5
Associated with nutritional deficiency, weakened immune system, anaemia, osteoporosis, and fertility issues. Common causes: insufficient caloric intake, malabsorption conditions (celiac disease, Crohn's), hyperthyroidism, or eating disorders. Action: consult a doctor to rule out underlying conditions; increase caloric intake through nutrient-dense foods; strength training to build muscle mass.
Normal weight — BMI 18.5 to 24.9
Associated with the lowest risk of weight-related health conditions. Note: a "normal" BMI does not guarantee good health — someone can have a normal BMI with high body fat % (called "skinny fat" or normal-weight obesity) if they have low muscle mass. Regular exercise and a balanced diet remain important even at a healthy BMI.
Overweight — BMI 25 to 29.9
Increased risk of type 2 diabetes, high blood pressure, sleep apnoea, fatty liver disease, and certain cancers. Research shows that losing just 5–10% of body weight (e.g. 4–8 kg for an 80 kg person) significantly reduces these risks. Even modest lifestyle changes — 150 minutes of moderate exercise per week plus calorie-conscious eating — produce measurable results within weeks.
Obese — BMI 30 and above: Obesity is further classified into three sub-classes: Class I (BMI 30–34.9), Class II (BMI 35–39.9), and Class III/Severe obesity (BMI 40+). Class III is sometimes called "morbid obesity." Health risks at this level include substantially elevated risk of cardiovascular disease, type 2 diabetes, stroke, certain cancers (breast, colon, endometrial), osteoarthritis, and respiratory complications. Medical consultation is strongly recommended — effective interventions include medically supervised caloric restriction, structured physical activity, behavioural therapy, and in some cases bariatric surgery.
BMI healthy weight ranges by height — quick reference table
These are the weight ranges that correspond to a "Normal weight" BMI of 18.5–24.9 for common heights. Use this as a practical reference alongside the calculator:
- 150 cm (4 ft 11 in): Normal weight = 41.6 kg to 56.1 kg
- 155 cm (5 ft 1 in): Normal weight = 44.4 kg to 59.9 kg
- 160 cm (5 ft 3 in): Normal weight = 47.4 kg to 63.8 kg
- 165 cm (5 ft 5 in): Normal weight = 50.3 kg to 67.8 kg
- 170 cm (5 ft 7 in): Normal weight = 53.5 kg to 72.0 kg
- 175 cm (5 ft 9 in): Normal weight = 56.7 kg to 76.3 kg
- 180 cm (5 ft 11 in): Normal weight = 59.9 kg to 80.9 kg
- 185 cm (6 ft 1 in): Normal weight = 63.3 kg to 85.3 kg
For Indian/Asian populations using the lower thresholds (18.5–22.9 for normal, 23–27.4 for overweight), the upper boundary for "normal" at each height is approximately 8–10% lower than the values shown above.
BMI for Indians and South Asians — why the thresholds are different
Multiple large-scale studies — including research published in The Lancet and by the Indian Council of Medical Research (ICMR) — have established that South Asians develop metabolic complications (insulin resistance, type 2 diabetes, hypertension) at significantly lower BMI values than populations of European descent. The reason: South Asians tend to accumulate more visceral fat (fat around internal organs) and less subcutaneous fat at the same BMI, and this visceral fat is more metabolically harmful.
The World Health Organization's expert consultation for Asian populations recommends these alternative cut-offs for South Asians (including Indians, Pakistanis, Bangladeshis, and Sri Lankans):
- Below 18.5: Underweight (same as global standard)
- 18.5 – 22.9: Normal weight (Asian standard — global standard goes to 24.9)
- 23.0 – 27.4: Overweight (Asian standard — global threshold starts at 25)
- 27.5 and above: Obese (Asian standard — global threshold is 30)
This means an Indian person with a BMI of 24 falls in the "Normal" range by global WHO standards — but in the "Overweight" range by Asian-specific guidelines. The Ministry of Health and Family Welfare (India) and the Indian Heart Association both recommend using 23 as the overweight threshold for Indians in clinical practice. This calculator uses the global WHO thresholds (as they are the universal standard), but the article on this page highlights the Asian-specific context so you can interpret your result accordingly.
Why BMI sometimes misleads — and better companion measurements
Athletes and muscular people
Muscle is denser than fat — 1 litre of muscle weighs approximately 1.06 kg, while 1 litre of fat weighs 0.9 kg. A bodybuilder or rugby player may have a BMI of 28–32 with very low body fat. The calculator cannot distinguish muscle from fat — it only sees total weight. If you are very active and muscular, your BMI likely overstates your health risk.
Older adults (60+)
Sarcopenia (age-related muscle loss) is common — people over 60 often lose 1–2% of muscle mass per year. This means an older person can have a "normal" BMI while having high body fat % and low functional muscle mass — a condition sometimes called "sarcopenic obesity." For older adults, physical function and waist circumference are more informative than BMI alone.
Use waist circumference alongside BMI
Waist circumference directly measures abdominal fat — the most metabolically dangerous fat type. WHO risk thresholds: Men: increased risk above 94 cm (37 in), high risk above 102 cm (40 in). Women: increased risk above 80 cm (31.5 in), high risk above 88 cm (34.6 in). For South Asians: Men above 90 cm and women above 80 cm are at increased risk. Measure at the navel level, not the belt line.
BMI vs body fat percentage — what is actually being measured
BMI estimates health risk indirectly via weight-to-height ratio. Body fat percentage (BF%) directly measures what fraction of your total weight is fat. Healthy BF% ranges differ by sex and age: For adult men: 8–19% is considered healthy, 20–24% is acceptable, 25%+ is obese. For adult women: 21–32% is healthy, 33–38% is acceptable, 39%+ is obese. BF% can be measured by DEXA scan (gold standard), hydrostatic weighing, bioelectrical impedance (BIA scales), or skinfold callipers. A BMI of 25 might correspond to anywhere from 15% body fat (a muscular person) to 30% body fat (a sedentary person with little muscle) — which is why BF% is the more precise metric when available.
What to do based on your BMI result
If you are underweight (BMI <18.5): Aim to increase caloric intake by 300–500 kcal/day above your maintenance level, focusing on protein (1.6–2.2 g/kg body weight/day) and complex carbohydrates. Add 3 sessions of strength training per week to gain muscle alongside weight. Rule out medical causes — thyroid disorders, malabsorption, and eating disorders are common causes of low BMI that require medical attention.
If you are in the normal range (BMI 18.5–24.9): Maintain current habits. The three pillars of staying healthy at a normal BMI: 150+ minutes of moderate aerobic activity per week (WHO recommendation), strength training 2+ days/week, and a diet rich in vegetables, whole grains, lean protein, and healthy fats. Monitor BMI periodically — age-related muscle loss can cause BMI to look stable while body fat is quietly increasing.
If you are overweight (BMI 25–29.9): A 500 kcal/day deficit produces approximately 0.5 kg weight loss per week. For an 80 kg person at BMI 27, losing 5–8 kg brings BMI into the normal range. Prioritise: reducing ultra-processed food and sugary drinks, increasing dietary fibre (target 25–35 g/day), adding 30 minutes of brisk walking daily, and sleeping 7–9 hours (poor sleep increases hunger hormones).
If you are obese (BMI ≥30): Medical supervision is recommended. Evidence-based interventions include: structured low-calorie or very-low-calorie diets (800–1,200 kcal/day) under medical monitoring; GLP-1 receptor agonist medications (semaglutide/Ozempic, liraglutide/Saxenda) now available in India and showing 10–15% weight loss in trials; and bariatric surgery for BMI ≥40 or BMI ≥35 with serious comorbidities. The most effective long-term approach combines diet, exercise, behavioural counselling, and medical support.
Free, instant, metric and imperial — no signup required.
Frequently asked questions
What is BMI and how is it calculated?
BMI (Body Mass Index) is a numerical value derived from your height and weight that indicates whether your weight is in a healthy range for your height. It was developed as a population-level screening tool, not as a clinical diagnostic. The formula is: BMI = weight (kg) ÷ height² (m²). Example: height 165 cm (1.65 m), weight 60 kg → BMI = 60 ÷ (1.65 × 1.65) = 60 ÷ 2.7225 = 22.0 (Normal weight). For imperial units: BMI = [weight (lbs) ÷ height² (inches²)] × 703. Example: 5 ft 5 in (65 inches), 132 lbs → BMI = (132 ÷ 4225) × 703 = 22.0. This calculator performs both conversions automatically. The WHO uses BMI as a primary screening tool because it requires only two measurements, has no equipment cost, and correlates reasonably well with body fat at the population level.
What are the WHO BMI categories, and what does each one mean for health?
Underweight (BMI <18.5): Associated with malnutrition, nutritional deficiencies, weakened immunity, and — in women — menstrual irregularities and increased risk of osteoporosis. Seek medical advice to rule out underlying conditions. Normal weight (BMI 18.5–24.9): Lowest statistical risk of weight-related health conditions. Maintain through balanced diet and regular physical activity. Overweight (BMI 25–29.9): Increased risk of type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea, and some cancers. A 5–10% reduction in body weight significantly reduces these risks. Obese Class I (BMI 30–34.9): High risk. Obese Class II (BMI 35–39.9): Very high risk. Obese Class III/Severe (BMI ≥40): Extremely high risk — medical intervention is recommended. Note: these are statistical correlations at the population level. Individual health depends on many factors beyond BMI — including blood pressure, blood glucose, cholesterol, physical fitness, diet quality, and family history.
What is a healthy BMI for Indians? Why is it different from the WHO standard?
For South Asians (Indians, Pakistanis, Bangladeshis, Sri Lankans), health organisations recommend lower BMI thresholds than the global WHO standard: Overweight starts at BMI 23 (not 25), and obese starts at BMI 27.5 (not 30). Why the difference? Research consistently shows that South Asians accumulate more visceral fat (fat around internal organs) and less subcutaneous fat (fat under the skin) at the same BMI compared to Europeans. Visceral fat is more metabolically active and harmful — it releases inflammatory cytokines and is directly linked to insulin resistance, type 2 diabetes, and cardiovascular disease. Studies from AIIMS, the Diabetes Foundation of India, and international journals including The Lancet and BMJ have confirmed that South Asians develop these metabolic complications at BMI levels where Europeans are still considered healthy. The Indian Ministry of Health, Indian Heart Association, and the Endocrine Society of India all recommend using 23 as the overweight threshold for Indians in clinical practice. In practical terms: an Indian person at BMI 24.5 falls in the "Normal" range by global standards but the "Overweight" range by Indian-specific guidelines — and should take the same preventive action as a European person at BMI 26.
Is BMI accurate for everyone? Who should not rely on it?
BMI has well-documented limitations for specific groups: Athletes and bodybuilders: Muscle is denser than fat. A male athlete at 180 cm and 90 kg has BMI 27.8 ("Overweight") but may have only 10–12% body fat. For this group, body fat percentage (via DEXA scan or BIA) is a far better metric. Older adults (60+): Age-related muscle loss (sarcopenia) means older people can have a "Normal" BMI while having 35%+ body fat and very little functional muscle. Waist circumference and physical function tests are more informative. Women vs men: Women naturally carry 6–11% more body fat than men at the same BMI — a woman at BMI 22 may have 28% body fat while a man at the same BMI may have only 18%. Pregnant women: BMI is not applicable during pregnancy — weight gain recommendations are based on pre-pregnancy BMI and gestational guidelines. Children and adolescents: BMI in children (under 18) must be interpreted using age- and sex-specific percentile charts (WHO Child Growth Standards or IAP Indian growth charts) — the adult thresholds (18.5, 25, 30) do not apply. For all these groups, BMI is best treated as one data point among several, not as a standalone verdict.
How do I convert my height and weight to use this calculator?
Height conversions for metric (cm): 5 ft = 152.4 cm. 5 ft 2 in = 157.5 cm. 5 ft 4 in = 162.6 cm. 5 ft 6 in = 167.6 cm. 5 ft 8 in = 172.7 cm. 5 ft 10 in = 177.8 cm. 6 ft = 182.9 cm. Formula: total inches × 2.54 = cm. Weight conversions for metric (kg): 100 lbs = 45.4 kg. 120 lbs = 54.4 kg. 140 lbs = 63.5 kg. 160 lbs = 72.6 kg. 180 lbs = 81.6 kg. Formula: lbs ÷ 2.205 = kg. However, you do not need to convert anything manually — this calculator has a built-in imperial mode. Click "Imperial (lbs, in)" at the top and enter your height in feet and inches separately and your weight in pounds directly. The calculator converts internally and shows the correct BMI.
How much weight do I need to lose (or gain) to reach a normal BMI?
Use this formula: Target weight (kg) = Target BMI × Height (m)². Example: You are 165 cm (1.65 m) tall with a current BMI of 28 (weight ≈ 76 kg). To reach the top of the Normal range (BMI 24.9): Target weight = 24.9 × (1.65 × 1.65) = 24.9 × 2.7225 = 67.8 kg. Weight to lose: 76 − 67.8 = 8.2 kg. At a sustainable deficit of 500 kcal/day (approximately 0.5 kg/week), this takes roughly 16 weeks. For South Asians aiming for the Asian threshold (BMI 22.9 or below): Target weight = 22.9 × 2.7225 = 62.3 kg — requires losing 13.7 kg from 76 kg. Use the calculator above to find your current BMI, then apply this formula to calculate your specific target weight. These are goals for healthy adults — consult a healthcare professional before starting any significant weight loss programme, especially at a calorie deficit exceeding 500 kcal/day.
Should I be worried if my BMI is in the "Overweight" range but I feel healthy?
Feeling well is important, but many metabolic conditions (pre-diabetes, hypertension, high cholesterol, fatty liver disease) have no symptoms in their early stages. Studies show that approximately 30–40% of people with BMI in the overweight range already have at least one metabolic abnormality, even without symptoms. For Indians specifically, the risk of type 2 diabetes rises sharply from BMI 23 onwards — India has the world's second-largest diabetic population, and a significant proportion are at "normal" or "overweight" BMI by global standards. The most useful step alongside checking your BMI: get basic blood tests done annually — fasting blood glucose, HbA1c, lipid profile, and blood pressure. These give a much more complete picture of your metabolic health than BMI alone. If all these are normal and you are physically active, your actual health risk may be lower than your BMI suggests. If they are borderline, your BMI is signalling correctly even if you feel fine.