BMI Calculator — Body Mass Index & Ideal Weight for Your Height

Body Mass Index (BMI) is a number calculated from a person's weight and height that provides a reliable indicator of body fatness. It was developed in 1832 by Belgian mathematician Adolphe Quetelet — which is why it is sometimes called the Quetelet Index. In 1995, the WHO officially adopted BMI as the standard screening tool for overweight and obesity in adults. Formula: BMI = weight (kg) ÷ height² (m). Example: 70 kg at 175 cm → BMI = 70 ÷ 3.0625 ≈ 22.9 — normal weight.

The WHO defines 8 BMI categories for adults: below 16 — severe underweight (very high risk); 16–16.9 — moderate underweight; 17–18.4 — mild underweight; 18.5–24.9 — normal weight (minimal health risk); 25–29.9 — overweight / pre-obese; 30–34.9 — obese class I; 35–39.9 — obese class II; 40 and above — morbid obesity class III. The "ideal" BMI for young adults is considered 22–23. Weight naturally increases with age, but no more than 2–3 kg per decade after 30.

BMI does not account for how fat is distributed in the body. Visceral fat — the fat stored around the abdomen — is more dangerous than subcutaneous fat and increases the risk of cardiovascular disease and type 2 diabetes independently of overall BMI. WHO thresholds: men — normal below 94 cm, elevated risk 94–102 cm, high risk above 102 cm; women — normal below 80 cm, 80–88 cm elevated, above 88 cm high risk. Measure waist circumference midway between the lower rib and the iliac crest.

BMI is a useful but imperfect tool. It does not account for body composition: muscle tissue is denser than fat, so athletes and bodybuilders often show "overweight" BMI values despite excellent health. BMI is also less accurate for: pregnant women; older adults (due to loss of muscle mass); children and adolescents (WHO age- and sex-specific percentile charts apply); certain ethnic groups (for people of Asian descent, overweight is defined as BMI ≥ 23 rather than 25). Always consult a doctor — BMI is a screening tool, not a diagnosis.

Ideal weight is the range where BMI falls within the normal zone (18.5–24.9). Formula: minimum weight = 18.5 × height²; maximum weight = 24.9 × height². Example at 5'7" (170 cm / 1.70 m): min = 18.5 × 2.89 = 53.5 kg (118 lb); max = 24.9 × 2.89 = 71.9 kg (159 lb). Our BMI calculator computes this range automatically for any height you enter.

A healthy BMI for women according to the WHO is 18.5 to 24.9 kg/m². Some experts consider 20–22 optimal for younger women. Keep in mind that BMI does not account for body frame — women with a larger bone structure may have a slightly higher BMI while carrying a healthy amount of body fat. The recommended waist circumference for women is below 80 cm (31.5 inches).

The healthy BMI range for men is also 18.5–24.9 kg/m². Because men naturally carry more muscle mass than women, a BMI closer to the upper end of the normal range may still indicate excellent health. Waist circumference should ideally stay below 94 cm (37 inches) for men.

A BMI of 30 or above is classified as obese by the WHO. Obesity is divided into three classes: Class I (30–34.9) — high risk; Class II (35–39.9) — very high risk; Class III or morbid obesity (40 and above) — extremely high risk. If your BMI is 30 or higher, a consultation with a doctor is strongly recommended.

Yes. This is known as "normal weight obesity" or "skinny fat". A person can have a normal BMI (18.5–24.9) but excess body fat due to low muscle mass. This is why waist circumference is an important additional metric. Women with a waist above 80 cm and men above 94 cm have elevated metabolic risk even with a normal BMI.

Formula: BMI = weight (kg) ÷ height (m)². Example: 68 kg at 165 cm (1.65 m). Calculation: 1.65² = 2.7225; 68 ÷ 2.7225 ≈ 24.98. Result — on the border between normal weight and overweight. In imperial units: BMI = (weight in pounds × 703) ÷ height in inches². Or simply use our BMI calculator above — enter your height and weight and get instant results.

The standard adult WHO BMI chart does not apply to children and adolescents under 18. For children, BMI is assessed using age- and sex-specific percentile charts. A value that is normal for an adult may indicate overweight in a 10-year-old — and vice versa. For assessing a child's weight, consult a paediatrician.

The standard WHO normal range (18.5–24.9) applies to all adults regardless of age. However, some researchers suggest that for people over 65, a slightly higher BMI of up to 27 may be associated with better outcomes due to protective effects on bone density and immune function. Conversely, excessive weight loss in older adults can be dangerous due to the risk of sarcopenia (muscle loss). Always consult your doctor for age-specific guidance.

A deficit of 500 calories per day generally leads to approximately 0.5 kg (1 lb) of weight loss per week — considered a safe and sustainable rate. Reducing intake below 1200 kcal for women or 1500 kcal for men can be harmful to health. For a personalised nutrition plan, consult a registered dietitian.