Question 1

How is BMI calculated?

Accepted Answer

BMI = weight (kg) ÷ height² (m²). Example: 75 kg, 1.75 m tall. BMI = 75 / (1.75 × 1.75) = 75 / 3.0625 = 24.49. In imperial: BMI = 703 × weight (lb) ÷ height² (in²). Example: 165 lb, 5 ft 9 in (69 inches). BMI = 703 × 165 / (69 × 69) = 115,995 / 4,761 = 24.37. The WHO BMI categories are: underweight < 18.5, normal weight 18.5–24.9, overweight 25–29.9, obese ≥ 30 (Class I: 30–34.9, Class II: 35–39.9, Class III: ≥ 40).

Question 2

What are the limitations of BMI?

Accepted Answer

BMI is a screening tool, not a diagnostic measure. Key limitations: (1) It cannot distinguish fat from muscle — athletes and heavily muscled people often have a high BMI despite low body fat; (2) It does not account for where fat is distributed — visceral fat (belly) is more harmful than subcutaneous fat; (3) It uses the same thresholds for men and women despite different body composition; (4) Research suggests different BMI thresholds for different ethnic groups — for example, Asian populations face elevated health risks at lower BMI values; (5) BMI is less useful for children, elderly, and pregnant women. Better measures: waist-to-height ratio, DEXA scan for body fat percentage, waist circumference.

Question 3

What is the healthy BMI range?

Accepted Answer

WHO adult BMI categories: Underweight: < 18.5 (severe < 16, moderate 16–17, mild 17–18.5); Normal / healthy weight: 18.5–24.9; Overweight: 25.0–29.9; Obese Class I: 30.0–34.9; Obese Class II: 35.0–39.9; Obese Class III (severe/morbid): ≥ 40.0. Note: for people of South Asian, East Asian and Southeast Asian ethnicity, many health organisations recommend lower action thresholds (overweight at BMI ≥ 23, obese at ≥ 27.5). The healthiest outcomes in large studies are typically associated with BMI 20–22 for men and 19–21 for women.

Question 4

What is the healthy weight range for my height?

Accepted Answer

The healthy weight range (BMI 18.5–24.9) for common heights: 5 ft (152 cm): 51–68 kg (112–150 lb); 5 ft 4 in (163 cm): 49–74 kg (108–163 lb); 5 ft 7 in (170 cm): 53–80 kg (118–176 lb); 5 ft 9 in (175 cm): 57–86 kg (125–189 lb); 5 ft 11 in (180 cm): 60–90 kg (132–198 lb); 6 ft (183 cm): 62–92 kg (136–203 lb). The BMI calculator shows your personal healthy weight range after calculating your BMI.

Category	BMI range	Health implications
Underweight (severe)	< 16.0	High risk of malnutrition, immune deficiency, anaemia
Underweight (moderate)	16.0–17.0	Elevated health risks; medical review recommended
Underweight (mild)	17.0–18.5	Some increased risk; may indicate poor nutrition
Normal / healthy ✓	18.5–24.9	Lowest risk for most health conditions
Overweight	25.0–29.9	Elevated risk of type 2 diabetes, heart disease
Obese Class I	30.0–34.9	High risk; lifestyle intervention recommended
Obese Class II	35.0–39.9	Very high risk; medical management often needed
Obese Class III	≥ 40.0	Extreme risk; potential surgical intervention considered

BMI Calculator

WHO BMI categories

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