Calculate your Body Mass Index and weight category
Body Mass Index (BMI) is a numerical value calculated from your height and weight. It provides a simple way to categorise weight relative to height and is used worldwide by healthcare professionals as a screening tool for weight-related health risks.
BMI = Weight (kg) ÷ Height² (m²)
A person weighing 75 kg and standing 175 cm tall has a BMI of 75 ÷ (1.75²) = 75 ÷ 3.0625 = 24.5 — within the normal range.
| BMI range | Category | Health risk |
|---|---|---|
| Below 18.5 | Underweight | Malnutrition, osteoporosis, immune issues |
| 18.5 – 24.9 | Normal weight | Lowest risk for most people |
| 25.0 – 29.9 | Overweight | Increased risk of cardiovascular disease |
| 30.0 – 34.9 | Obese (Class I) | High risk — metabolic syndrome common |
| 35.0 – 39.9 | Obese (Class II) | Very high risk |
| 40.0+ | Obese (Class III) | Severe risk — medical intervention often needed |
| Height | Minimum healthy weight | Maximum healthy weight |
|---|---|---|
| 155 cm (5'1") | 44 kg (97 lb) | 60 kg (132 lb) |
| 160 cm (5'3") | 47 kg (104 lb) | 64 kg (141 lb) |
| 165 cm (5'5") | 50 kg (111 lb) | 68 kg (149 lb) |
| 170 cm (5'7") | 53 kg (118 lb) | 72 kg (159 lb) |
| 175 cm (5'9") | 57 kg (125 lb) | 76 kg (168 lb) |
| 180 cm (5'11") | 60 kg (132 lb) | 81 kg (178 lb) |
| 185 cm (6'1") | 63 kg (140 lb) | 86 kg (189 lb) |
| 190 cm (6'3") | 67 kg (147 lb) | 91 kg (200 lb) |
BMI is a useful population-level screening tool but has significant individual limitations. It does not distinguish between fat mass and muscle mass — a professional athlete with very low body fat can have a BMI in the overweight range due to muscle density. Conversely, someone with a normal BMI can have unhealthy levels of visceral fat (the dangerous fat around internal organs).
BMI also does not account for age-related changes in body composition, ethnic differences in body fat distribution, or sex differences beyond what the formula captures. Asian populations, for example, face increased health risks at lower BMI thresholds — some health organisations use 23.0 as the overweight cut-off for Asian adults rather than 25.0.
For a more complete picture, combine BMI with waist circumference (a direct indicator of visceral fat), waist-to-height ratio (should be below 0.5), and blood pressure, blood glucose, and cholesterol levels. These together give a far more accurate picture of cardiometabolic risk than BMI alone.
The WHO defines 18.5–24.9 as the healthy range for most adults. However, optimal BMI varies by age, sex, and ethnicity. Some research suggests 22–23 is associated with the lowest all-cause mortality in Western populations.
The BMI formula is the same for men and women, but body composition differs — women naturally carry more body fat than men at the same BMI. At a BMI of 25, a woman typically has a higher body fat percentage than a man. Some researchers argue for sex-specific BMI thresholds, though this is not yet standard practice.
Children's BMI (called BMI-for-age) is interpreted differently — it is compared to age and sex-specific percentiles rather than fixed thresholds. A child's BMI percentile is more meaningful than the raw number. Consult a paediatrician for interpretation of children's BMI.
Yes — this is called normal-weight obesity or skinny fat. People with normal BMI but high body fat percentage and low muscle mass can have significant metabolic risk factors. Waist circumference and activity level are important additional indicators.
BMI decreases when you lose fat mass relative to height. This is achieved through a sustained calorie deficit (eating less than you burn), increased physical activity, or ideally both. Strength training preserves muscle while losing fat, which improves body composition even if BMI changes slowly.