BMI Calculator
Calculate your Body Mass Index — find your health category and ideal weight range
tuneBody Measurements
Unit System
Weight (kg)
kg
Height (cm)
cm
Gender (optional)
Age (optional)
yrs
Your BMI
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—
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BMI Scale
Underweight
<18.5 Normal
18.5–24.9 Overweight
25–29.9 Obese
≥30
<18.5 Normal
18.5–24.9 Overweight
25–29.9 Obese
≥30
Weight
—
Height
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Ideal Weight Range
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Healthy BMI 18.5–24.9
Weight to Lose/Gain
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BMI Categories (WHO)
| BMI Range | Category | Risk |
|---|---|---|
| < 18.5 | Underweight | Moderate |
| 18.5–24.9 | Normal | Minimal |
| 25.0–29.9 | Overweight | Increased |
| 30.0–34.9 | Obese I | High |
| 35.0–39.9 | Obese II | Very High |
| ≥ 40.0 | Obese III | Extremely High |
What is a BMI Calculator?
Body Mass Index (BMI) is a simple measure calculated from your height and weight that indicates whether you are underweight, normal weight, overweight, or obese. It is widely used by doctors and health professionals as an initial screening tool to assess weight-related health risks.
For adults, a BMI below 18.5 is underweight, 18.5–24.9 is normal, 25–29.9 is overweight, and 30+ is obese. It's a quick guide — but factors like muscle mass and bone density are not captured. Athletes often have high BMI despite being healthy.
lightbulb Example Calculation
Scenario: Mrs. Anjali Rao, 32-year-old schoolteacher in Pune — weighs 68 kg, height 163 cm (5'4"), wants to check if she's in a healthy weight range before starting a diet plan
1BMI = weight (kg) / height² (m²) = 68 / (1.63 × 1.63) = 68 / 2.6569 = 25.59
2BMI 25.59 falls in the 25–29.9 range → "Overweight"
3Ideal weight for 163 cm: BMI 18.5–24.9 → 49 kg to 66 kg range
✓ Result: Anjali's BMI is 25.6 — just above normal. Ideal weight range: 49–66 kg. Losing 3–4 kg brings her to healthy range.
help_outlineHow to Use the BMI Calculator
- Select your preferred unit system — Metric (kg and cm) for most users, or Imperial (lbs, feet, and inches).
- Enter your weight in kilograms or pounds as applicable.
- Enter your height in centimetres, or feet and inches for imperial — the calculator converts automatically.
- Optionally enter your age and gender for additional context, though BMI itself is computed only from height and weight.
- Click Calculate BMI to see your BMI value, WHO health category, ideal weight range for your height, and how much weight to lose or gain to reach the normal range.
Benefits
- Instant health category classification — underweight, normal, overweight, or obese
- Shows ideal weight range for your height based on WHO's normal BMI (18.5–24.9)
- Supports both metric and imperial units for worldwide usability
- Displays the BMI scale visually to contextualise your position
- Quick pre-screening tool before a medical check-up or starting a fitness program
Key Terms
- BMI (Body Mass Index)
- Weight in kilograms divided by height in metres squared (kg/m²). A widely used proxy for body fatness in adults.
- Underweight
- BMI below 18.5 — associated with malnutrition, hormonal imbalances, and weakened immunity.
- Normal Weight
- BMI 18.5–24.9 — associated with lowest risk of weight-related diseases according to WHO.
- Overweight
- BMI 25–29.9 — indicates excess weight relative to height; increased risk of type 2 diabetes, heart disease, and hypertension.
- Obesity
- BMI 30 and above, classified into Class I (30–34.9), Class II (35–39.9), and Class III/Morbid Obesity (40+) with progressively higher health risks.
quizFrequently Asked Questions
Is BMI accurate for athletes or very muscular people?
BMI can misclassify very muscular individuals as overweight or obese because it does not distinguish between fat mass and muscle mass. A bodybuilder with 8% body fat and high muscle mass may have a BMI over 30, which would be classified as obese — clearly inaccurate. For such individuals, body fat percentage measurements like DEXA scans or skinfold calipers are more meaningful.
What is a healthy BMI specifically for Indians?
The WHO standard uses 18.5–24.9 as normal. However, research has shown that South Asians, including Indians, tend to develop metabolic risk factors (diabetes, cardiovascular disease) at lower BMI values. Some Indian health guidelines suggest a normal range of 18–22.9 for Asians, with overweight beginning at 23. Using the Asian cutoff, even a BMI of 23.5 warrants monitoring for Indians.
How do I calculate BMI manually?
BMI = Weight (kg) ÷ [Height (m)]². Convert your height to metres first (e.g., 170 cm = 1.70 m), then square it (1.70 × 1.70 = 2.89), and divide your weight by this value. For example, 75 kg ÷ 2.89 = BMI 25.95. For imperial units, BMI = [Weight (lbs) ÷ Height (inches)²] × 703.
Does BMI apply to children?
The standard adult BMI chart does not apply to children and teenagers. For those under 18, BMI-for-age percentiles are used instead, comparing the child's BMI to others of the same age and sex. Paediatricians use these growth charts — available from WHO and IAP (Indian Academy of Pediatrics) — to assess whether a child's weight is appropriate for their age and height.
What should I do if my BMI is outside the normal range?
A BMI outside the normal range (18.5–24.9) is a signal to consult a healthcare professional, not a diagnosis. For overweight/obese individuals, a doctor or dietitian can assess metabolic health markers (blood sugar, lipids, blood pressure) and recommend lifestyle interventions. For underweight individuals, investigating the underlying cause and increasing nutritional intake under medical supervision is advisable.
Can BMI vary between men and women with the same score?
The BMI formula and WHO categories are the same for adult men and women — the normal range is 18.5–24.9 for both. However, at the same BMI, women naturally have higher body fat percentage than men due to physiological differences. A woman with BMI 22 has more body fat than a man with BMI 22. This is why some clinicians use sex-specific body fat tables alongside BMI for a fuller picture.